SOIL ACIDITY - publication.eiar.gov.et:8080

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SOIL ACIDITY MANAGEMENT 1 SOIL ACIDITY MANAGEMENT SOIL ACIDITY MANAGEMENT የኢትዮጵያ የግብርና ምርምር ኢንስቲትዩት

Transcript of SOIL ACIDITY - publication.eiar.gov.et:8080

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SOIL ACIDITY MANAGEMENT 1

SOIL ACIDITY MANAGEMENT

SOIL ACIDITY MANAGEMENT

የኢትዮጵያ የግብርና ምርምር ኢንስቲትዩት

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©EIAR, 2019Website: http://www.eiar.gov.etTel: +251-11-6462633Fax: +251-11-6461294P.O.Box: 2003Addis Ababa, Ethiopia

Copyediting and Design: Abebe Kirub Cover Design: Elizabeth Baslyos

ISBN: 9789994466597

Correct Citation

Getachew Agegnehu, Chilot Yirga , andTeklu Erkossa. 2019. Soil Acidity Management. Ethiopian Institute of Agricultural Research (EIAR). Addis Ababa, Ethiopia

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SOIL ACIDITY MANAGEMENT

Getachew Agegnehu Chilot Yirga

Teklu Erkossa

Our partner :

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C O N T E N T SPREFACE ......................................................................................................... IFOREWORD .................................................................................................... IIINTRODUCTION ............................................................................................ 1Literature Search and Data Processing .............................................................................................. 3

EXTENT OF SOIL ACIDITY ............................................................................... 4MAJOR ACID SOILS ........................................................................................ 7CAUSES OF SOIL ACIDITY ............................................................................. 8Climate ......................................................................................................................................................... 8

Acidic parent material furnishing aluminum and silicon ions ....................................................... 8

Application of ammonium fertilizers ................................................................................................... 9

Decomposition of organic matter ......................................................................................................... 9

Removal of elements through harvest of high yielding crops ...................................................... 9

Low buffer capacity from little clay and organic matter ............................................................... 11

Alumino-silicate minerals ..................................................................................................................... 11

EFFECT OF SOIL ACIDITY ON NUTRIENT AVAILABILITY AND CROP YIELD ........ 12Types of soil acidity ................................................................................................................................ 12

Effect of soil acidity on nutrient availability and crop yield ........................................................ 13

MANAGEMENT OF SOIL ACIDITY ................................................................. 16Liming ......................................................................................................................................................... 16

Amount of lime required .................................................................................................................... 18

Methods for estimating lime requirements .................................................................... 18

Length of time for lime to work ........................................................................................................ 19

Frequency of liming ............................................................................................................................. 20

Effect of lime on soil acidity and crop yield .................................................................................. 20

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C O N T E N T SIntegrated soil fertility management (ISFM) ................................................................................... 24

Management of acid soils using acid tolerant crop varieties ..................................................... 25

Management of sub-soil acidity ......................................................................................................... 27

EXPERIENCE FROM BRAZIL ........................................................................ 31Natural resource evaluation ................................................................................................................. 32

Soil and water management ................................................................................................................ 32

Production system ................................................................................................................................. 33

POLICY CONSIDERATIONS ........................................................................... 35Benefits of amending acid soils with lime ........................................................................................ 35

Value chain and transaction costs of lime crushing ..................................................................... 39

Promotion of ISFM Approches ........................................................................................................... 43

CONCLUSION ............................................................................................... 45REFERENCES ............................................................................................... 46INDEX ........................................................................................................... 55

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SOIL ACIDITY MANAGEMENT I

PREFACEEthiopia faces a wide range of issues in soil fertility that requires approaches beyond inorganic fertilizer applications. The core soil-related constraints are soil erosion, soil acidification, depletion of organic matter, deterioration of soil biophysical properties, and salinity. Soil acidity and associated low soil nutrient are major constraints to crop production.

This publication provides ample information on causes, effects, and management of soil acidity, which is based on a review and synthesis of a wide range of literature resources. The publication supports the need for reclamation of soil acidity and significant improvements in soil fertility taking into account the country’s diverse agro-ecologies, cropping systems, crop and soil types, and climate. The publication clearly indicates that reclamation measures for soil acidity are critical to achieving the objectives of higher crop yields contained in the strategies of the agricultural sector of the Government of Ethiopia and its development partners. Attention to acid soil management, in which the soil acidity is controlled or monitored carefully, has grown in research and practice. All of these situations require knowledge of soil fertility and plant nutrient management.

The experience of Brazil also suggests that a sound knowledge and better understanding of chemical characteristics of acid soils are vital for proper management for increased and sustainable crop production. It also gives information on how to assess and manage soil acidity by farmers, agricultural advisers, soil scientists, and agronomists.

The authors would like to acknowledge the German Technical Cooperation (GIZ) for supporting to publish this handbook. Abebe Kirub is highly appreciated for editing and designing the publication. Our appreciation also goes to Elizabeth Baslyos for managing the production of the publication.

Authors

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SOIL ACIDITY MANAGEMENT II

FOREWORDSoil acidity is one of the major constraints affecting crop productivity. It affects about 43% of the cultivated land in humid and sub-humid highlands of Ethiopia. To fulfill the increasing demand for food and raw materials, soil health and fertility has remained as the major factor to increase and sustain crop yields. This calls for proper use of knowledge of soil acidity and its amelioration to maximize agricultural productivity. Farmers require simple and sustainable techniques to amend acid soils and improve yields of crops of their choices. Recommendations on reclamation of acid soils need to change with new developments, such as liming, use of acid-tolerant crop varieties, integrated soil fertility management, and better methods of estimating lime requirements. Liming has played an important role in raising soil pH and enhancing crop productivity. In Ethiopia, the gap between potential and actual yield is very wide because of soil acidity and associated nutrient availability. Acidic soils are not responsive to the application of inorganic fertilizers without amendments-it is simply wastage of resources. Thus, developing effective and efficient acid soil management practices is indispensable for enhancing crop productivity and thereby sustaining yield gains.The Natural Resources Management Research Directorate of the Ethiopian Institute of Agricultural Research has been conducting research on soil and water resources to enhance and maintain the overall resource base, improve and sustain agricultural productivity in the country. This publication reviews the causes and effects of soil acidity and its subsequent effect on soil fertility and crop yield. It also provides important information on management options to amend soil acidity and improve the entire fertility of soils, and other organic amendments that can be applied to remedy soil acidity to the desired pH level and improve soil quality. Integrated acid soil management enhances the stability of yields and maximizes nutrient use efficiency. The information contained in this publication unassumingly serves the interests of policymakers, researchers, students, agronomists and users associated with acid soils management.

Mandefro Nigussie (PhD)Director GeneralEthiopian Institute of Agricultural Research (EIAR)

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1INTRODUCTION

Soil acidity is among the major land degradation problems, which affects ~50% of the world’s potentially arable soils (Kochian et al., 2004). Naturally, soils tend to become acid because of the leaching mechanism of carbonic acid (CO2 dissolved in rainwater). Acidification continues until a balance is reached between removal and replacement. Basic cations such as calcium (Ca) and magnesium (Mg) are removed through leaching and crop harvest but at the same time these bases are replaced due to organic matter decomposition and from the weathering of minerals (Abebe, 2007; Sanchez, 1977). Geologically, soil acidity increases as rainfall increases. The availability of micronutrients such as Aluminum (Al), manganese (Mn) and iron (Fe) increases as the pH decreases. The major causes for soils to become acid are high rainfall and leaching, acidic parent material, organic matter decay, and harvest of high yielding crops (Eswaran et al., 1997b; Von Uexküll and Mutert, 1995). Crop management practices, removal of organic matter, continuous application of acid forming fertilizers and contact exchange between exchangeable hydrogen on root surfaces and the bases in exchangeable form on soils, microbial production of nitric and sulfuric acids can also contribute to soil acidity (Behera and Shukla, 2015; Fageria and Nascente, 2014). Roem and Berendse (2000) indicated that increasing N: P and N: K ratios appear to have adverse effects on the abundance of endangered species owing to soil acidification.

In the humid tropics, soils become acidic naturally due to leaching of basic cations under high rainfall conditions. At pH below 5, Al is soluble in water and becomes the dominant ion in the soil solution. In acid soils, excess Al primarily injures the root apex and inhibits root elongation (Sivaguru and Horst, 1998). The poor root growth leads to reduced water and nutrient uptake, and as a result crops grown on acid soils are constrained with poor nutrients and water availability. The net effect of which is reduced growth and yield of crops (Marschner, 2011; Wang et al., 2006). Soil acidity is expanding in scope and magnitude in Ethiopia, severely limiting crop production. For example, in some barley, wheat and faba bean growing areas of central and southern Ethiopian highlands, farmers have shifted to producing oats which is more tolerant to soil acidity than wheat and barley (Haile and Boke, 2009).

The main soil forming factors giving rise to increase in soil acidity involve climatic factors such as rainfall, temperature, topographic and morphological features (Abebe, 2007; Brady and Weil, 2016). Nitisol/Oxisol areas are the main soil classes dominated by soil acidity. In Ethiopia, these soils are predominantly acidic and more than 80% of the landmasses originated from Nitisol are acidic. Some of the well-known areas severely affected by soil acidity in Ethiopia include Gimbi, Nedjo, Hosanna, Sodo, Endibir, Chencha, Hageremariam and Awi (Abebe, 2007; Sertsu and Ali, 1983). Generally, soils developed on non-calcareous parent materials are inherently acidic. Acid Nitisols (pH <5.5) occur widely in Ethiopian highlands where the rainfall intensity is high and crop cultivation has gone for many years (Agegnehu and Bekele, 2005a; Zeleke et al., 2010).

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SOIL ACIDITY MANAGEMENT 2

The management of acid soils is the major problem area in the humid tropics. The identification and description of a problem area, however, does not justify a major research effort. An in-depth analysis of our present knowledge of soil processes related to soil acidity and the management of acid soils is required (Fageria and Baligar, 2008). Although many research related to the management of acid soils have been conducted in South America , Africa (Eswaran et al., 1997a; Tully et al., 2015), Asia and Australia (Bai et al., 2008; Eswaran et al., 1997b), there is no more detailed information and understanding of the problem related to the management of acid soils and different management options. The focus of MAS should be developing appropriate technologies for sustainable management of soil and water resources of acid soil agro-ecosystems. Indiscriminate clearing, inappropriate land use and mismanagement of soil and water resources are degrading the resource base. The loss of top soil means declining soil fertility, deterioration of soil structure and lower productivity (Bronick and Lal, 2005; Lal, 2015). Intensive agriculture in such areas is a viable and attractive alternative to farming the marginal lands of hillsides. Thus, management of acid soils (MAS) needs to emphasize strategic research, integrating soil and water management with improved germplasm to generate prototype and environmentally benign technologies for sustained food production within a framework of appropriate socioeconomic and policy considerations. Such technologies need to focus on organic matter depletion in acid soil, erosion control in highlands, and reclamation of acid soils. Analysis of relationships among policies and land-use strategies needs to be made to assess the potential impact of improved technologies on production and the environment (Lal, 2015; Thomas, 1995).

The ultimate objective of MAS should be increasing agricultural productivity to meet the needs of a growing population, while maintaining or improving the natural resource base. Although the focus is to alleviate biophysical constraints on soil and water resources, implementing improved technologies requires appropriate socioeconomic and policy frameworks and active participation of farmers. Among the various opportunities sought to increase agricultural development, exploitation of degraded lands devoid of crop production as consequence of soil acidity is one of the area of priority to tackle. However, the research and development approaches used so far gave little attention to this critical problem and unable to develop an integrated solution to curb its progress. Now the extent of the problem has been realized and there is a need to give emphasis to minimize its adverse impact and foster its contribution to food production and natural resource management. The objective of this paper is, therefore, to review the cause and effects of soil acidity and its mitigation measures achieved through research and development in the tropical agro-ecosystems.

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Literature Search and Data Processing

A literature search was conducted through the Web of Science (apps.webofknowledge.com), Google Scholar (scholar.google.com), AGRIS (agris.fao.org), Research Gate (https://www.researchgate.net), the Ethiopian Society of Soil Science (www.esss.org.et), and libraries of the Ethiopian Institute of Agricultural Research (EIAR) and National Soils Research Center. We searched the literature published up to 2017, using “soil acidity”, “management of soil acidity”, “integrated soil fertility management”, and “liming” as key terms. Although over 760 papers were retrieved, we focused on those reporting empirical results on soil acidity and its management, and thus about 130 publications were used to develop this review paper.

Individual articles from the collected literature were grouped with respect to research objectives and experimental types. Research objectives were further sub-categorized into articles focusing on organic and inorganic nutrient sources, including lime, and other management practices such as acid tolerant crop species and varieties. Crops tested for soil acidity tolerance in the field were cereals (grain crops, such as wheat, maize, and barley), food legumes (faba bean and soybean), and root crops (potato). The information collected from the published literature was organized into an archived database. For some data, statistical analysis was performed using SAS-STAT software and graphical presentations were constructed using Microsoft Excel 2010.

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2EXTENT OF SOIL ACIDITY

Soil quality is the ability of the soil to perform its functions in a sustainable manner (Lal, 2015). Soil biophysical and chemical properties change with time and changes are accelerated through management practices. Soil acidity is among the major land degradation problem worldwide. About 30% of the ice-free soils (close to 4 billion ha) in the world are acidic (Sumner and Noble, 2003). Tropical and sub-tropical regions as well as areas with moderate climatic conditions are mostly affected by soil acidity. Worldwide, 32% of all arable land is acid (Eswaran et al., 1997a). Almost two-third of all acidic soils in the world belongs to Ultisols, Entisols and Oxisols (Rengel, 2011).

Oxisols (also referred to Ferralsols) occupy about 3.75 million km2 or 14.3% of the total land area of Africa. About 10.76 million km2 or 35% of the total area of land in Africa is characterized by P fixation, i.e. from slight to high fixation, and out of this 8.23 million km2 is typified by high P fixation (Eswaran et al., 1997b). Similarly, tropical American soils are largely acid and low in reserves of nutrients available to plants. The critical need to increase agricultural production causes great pressure on fragile soils and natural resources. Such soils contain toxic levels of Al and Mn, are prone to compaction and erode easily (Thomas, 1995). For example, the ‘Cerado’ (acid savanna soils) affects an area of 207 million ha in Brazil alone (Fageria and Nascente, 2014; Thomas, 1995). The Oxisols (dusk red Latosols, dark red Latosols, red yellow Latosols, and yellow Latosols) are the dominant soils, with about 98 million ha (Thomas, 1995). They are very weathered deep, acid soils, with a low availability of nutrients, but with good physical properties due to the predominance of 1:1 clay minerals, and Fe and Al oxides in the fraction (de Sant-Anna et al., 2017).

Land degradation is a critical challenge, substantially affecting agricultural productivity and rural livelihoods in Ethiopia (Yirga and Hassan, 2010), especially serious in the highlands, which is 44% of the total area of the country where human and livestock pressure is high (Amede et al., 2001). It is home to 90% of the total human population; 95% of the land under crops and 75% of livestock are also located in this area (Amede et al., 2001). The impact of land degradation has put at risk the livelihoods, economic well-being, and nutritional status of several people in the country (Tadesse, 2001). Land degradation not only reduces the productive capacity of agricultural land, rangelands and forest resources but also considerably impacts on biodiversity (Akhtar et al., 2011). It adversely affects the ecological integrity and productivity of large areas of land, or landscapes under human use. Soil acidity and associated low nutrient availability are key constraints to crop production in acidic soils, mainly Nitisols of Ethiopian highlands (Zeleke et al., 2010). Haile et al. (2017) estimated that ~43% of the Ethiopian cultivated land is affected by soil acidity). The extent of soil acidity in Ethiopia is shown in Figure 1. About 28.1% of these soils are dominated by strong acid soils (pH 4.1-5.5) (ATA, 2014). Strongly acidic soils are usually infertile because of the possible Al and Mn toxicities, and Ca, Mg, P, and molybdenum (Mo) deficiencies (Barber, 1984).

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Figure 1. Extent and distribution of soil acidity (ATA, 2014) in Ethiopia

The clay mineralogy, pH, presence of oxides and hydroxides of Fe and Al and content of amorphous materials seem to be the dominant factors affecting P sorption. In the case of highly weathered soils of Chencha, Nedjo and Endibir, where the dominant minerals are Gibbsite, Goethite, Kaolinite and desilicated amorphous materials, P sorption is high to very high (Table 1). The mechanism of phosphate adsorption is considered to be mainly through replacement of hydroxyl ions on crystal lattices, and hydrated Fe and Al by phosphate ions (Adams, 1990; Velayutham, 1980). Phosphorus sorption capacity increases with increasing acidity (decreasing pH value). For instance, soils from rift valley of Ethiopia had the lowest P sorption, which are the least weathered (with a pH value of 7.8). In contrast, the soil from the highlands of Ethiopia (e.g. Chencha) had the highest P sorption, which has a pH of 4.5, and has higher content of gibbsite, goethite and amorphous materials than other sites except Endibir for amorphous materials (Sertsu and Ali, 1983).

According to Duffera and Robarge (1999), between 70 and 75% of the reddish-brown agricultural soils of the Ethiopian highlands are highly deficient in P. Bekele and Höfner (1993) reported that yields could be doubled, in some cases tripled, with P application. However, the high costs of high grade, water-soluble P fertilizers, coupled with the high fixing capacities of these soils for P, caused agronomic and economic constraints to crop production. Alisols, Nitisols and Fluvisols are among the dominant acidic soils in the southern region, including Hosanna, Sodo, Chencha, and Hagereselam. A number of adverse effects such as loss of crop diversity, decline in the yield of existing crops, lack of response to N and P fertilizers, and complete failure of crop yields were reported. Yields of barley, wheat, and other crops are extremely low under application of optimum rate of NP fertilizers on Alisols of Chencha (Haile and Boke, 2011).

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SOIL ACIDITY MANAGEMENT 6

Table 1. Amount of P sorbed by some Ethiopian soils at the standard solution P of 0.2 mg kg-1

Soil origin

Sorbed P

pH Fe2O3(%)

Exch. Al (cmol (+) kg-1)

Amorphous material (%)

Gibbsite and Goethite (%)mg kg-1 kg ha-1

Chencha 1200 2400 4.5 11.7 0.40 51 10

Nedjo 950 1900 4.4 16.1 6.16 32 12

Endibir 800 1600 4.8 11.7 1.69 61 0

Melko 600 1200 5.2 15.8 0.37 ND ND

Bako 400 900 6.6 14.4 0.02 41 15

Melkassa 150 300 7.8 0.20 Tr. ND ND

ND: Not determined; Tr: Trace. Source: Sertsu and Ali (1983).

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3MAJOR ACID SOILS

The predominant soil associations are Dystric Nitisols and Orthic Acrisols with inclusions of Dystric Cambisols and Lithosols on the steepest slopes (Abebe, 1998, 2007). Eutric Nitisol is the dominant soil type as Nitisol in the central highlands of Ethiopia where soil acidity is the problem. Nitisol is the major soil unit that covers the western part of Ethiopia (Abebe, 2007). The soil develops on a wide range of parent materials, such as volcanic, metamorphic, granitic, and felsic materials, sandstones and limestone. The soil occurs on the gently sloping to steep land, on flat and undulating lands, usually with other types of soil units such as Gleysols or Vertisols. On the other hand, the steeper slops are usually covered with shallow soils such as Cambisols and Luvisols (Abebe, 1998, 2007). Nitisols are reddish brown to red clay, which have been formed by strong weathering under humid conditions, which are well drained and have a strong tendency to erosion, and their fertility depends on the base saturation and is valued to be medium to high. Nitisols have very good potential for agriculture; they have a stable structure and a high water storage capacity. Workability on these soils does not create any problem even shortly after precipitation or in the dry season, land can be prepared without difficulty. These soils have a rather low CEC for their clay content and available P are usually very low (Abebe, 2007).

Nitisols have three sub-soil units, i.e. Eutric, Dystric and Humic Nitisols. Dystric Nitisol contains relatively high organic matter content in the top layer and high base saturation in the soil profile, especially in the A and B-horizons, indicating the high fertility status of the soil. Eutric Nitisol has red to dusky red lower laying horizon, with similar fertility status to that of the Dystric Nitisol. Nitisols are found in areas where the slope is between 2-16% on undulating plains, low plateaus, gentle hills and mountains side slopes of all areas. The problem of acidity is closely related to these soil types due to their geographical location, intensive cultivation, and inappropriate farm management practices (Abebe, 2007).

Acrisols are generally developed from acidic parent material, which occur in the high rainfall areas associated with Nitisols and Cambisols. These soils are found on moderate to steep slopes. They are moderately suited for agriculture, partly they are cultivated, and partly they are left under natural vegetation for grazing purposes. Base saturation is generally low, and pH value is generally below neutrality. Acrisols are the results of strong weathering and depletion of bases by leaching (Abebe, 1998).

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4CAUSES OF SOIL ACIDITY

Soil acidification is a complex set of process resulting in the formation of an acid soil. In the broadest sense, it can be considered as the summation of natural and anthropogenic processes that lower down the pH of soil solution (Krug and Frink, 1983). Inefficient use of nitrogen is one of the causes of soil acidification, followed by the export of alkalinity in produce (Guo et al., 2010). Ammonium based fertilizers are major contributors to soil acidification. Ammonium nitrogen is readily converted to nitrate and hydrogen ions in the soil. It has been recognized that there are several causes for soils to become acidic.

Climate

It has been well recognized that in soils of dry region a large supply of bases is usually present, since little water passes through the soil. With an increase in rainfall, the contents of soluble salts are reduced to a low level, and any calcium carbonate and gypsum present are removed. With further increase in rainfall, a point is reached at which the rate of removal of bases exceeds the rate of their liberation from non-exchangeable forms. Wet climates have a greater potential for acidic soils (Sanchez, 1977; Tadesse, 2001). Over time, excessive rainfall leaches the soil profile’s basic elements (Ca, Mg, Na, and K) that prevent soil acidity. High rainfall leaches soluble nutrients such as Ca and Mg which are specifically replaced by Al from the exchange sites (Brady and Weil, 2016).

Acidic parent material furnishing aluminum and silicon ions

Rocks containing an excess of quartz or of silica as compared to their content of basic materials or of basic elements are categorized as acid rocks; for example, granite and rhyolite. When rocks that are deficient in bases are disintegrated or decomposed in the process of the accumulation of soil material is acidic, despite no loss of base during the process of soil formation. Soils that develop from weathered granite are likely to be more acidic than those developed from shale or limestone. There are large areas of siliceous and sandy soils produced from acid parent rocks, which have always been in need of lime. However, most acid soils have been developed as a result of leaching losses and crop removal of bases (Brady and Weil, 2016).

The inherent fertility of Ethiopian soils developed under varied parent materials and climate varies depending on the origin and composition of the materials (Table 2). For instance, soils developed from sandstones are poor sandy soils, whereas the inherent soil fertility developed over basic parent materials is relatively high (Woldeab and Mamo, 1991). In alluvium plains, alluvium becomes rich and fertile if it originates from relatively young materials, and less fertile if it originates from highly weathered surfaces. The pH values in the majority of soils are in the range of 4.5 to 6.5. In most cases, soils found in high-altitude areas of the country are acidic in reaction, poor in exchangeable cations and low in base saturation (Bekele and Höfner, 1993; Regassa and Agegnehu, 2011).

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SOIL ACIDITY MANAGEMENT 9

Application of ammonium fertilizers

Continuous application of inorganic fertilizer without soil test, in the end, can increase soil acidity. The use of N fertilizers in ammonia form is a source of acidification (Fageria and Nascente, 2014; Guo et al., 2010). When ammonium fertilizers are applied to the soil, acidity is produced, but the form of N removed by the crop is similar to that found in fertilizer. Hydrogen is added in the form of ammonia-based fertilizers (NH4), urea-based fertilizers [(CO (NH2)2], and as proteins (amino acid) in organic fertilizers. Transformation of such sources of N fertilizers into nitrate (NO3) releases hydrogen ions (H+) to create soil acidity. In reality, N fertilizer increases soil acidity by increasing crop yields, thereby increasing the amount of basic elements being removed. Hence, application of fertilizers containing NH4 or even adding large quantities of organic matter to a soil can ultimately increase soil acidity and lower pH (Guo et al., 2010; Hue, 1992).

Decomposition of organic matter

The decomposition of organic matter produces H+ ions, which are responsible for acidity. The development of soil acidity from the decomposition of organic matter is insignificant in the short-term. Large quantities of carbonic acid produced by microorganisms and higher plants including through other physicochemical and biological processes are the causes of soil acidity although the effect from its dissociation is relatively small as most of it is lost to the atmosphere as CO2 (Kochian et al., 2004; Paul, 2014). Soil organic matter or humus contains reactive carboxylic, enolic and phenolic groups that behave as weak acids. During their dissociation they release H+ ions. Further, the formation of CO2 and organic acids during the decomposition also result in replacement of bases on exchange complex with H+ ions (Somani et al., 1996). Removal of elements through harvest of high yielding crops

Removal of elements, especially from soils with small reservoir of bases due to the harvest of high yielding crops is responsible for soil acidity. When soils are worked mechanically and crops are grown the balance is disturbed and the soils become more acid. This is the result of base cations being removed with crops and the simultaneous increase of leaching which takes place when soils are disturbed and worked (Brady and Weil, 2016; Fageria, 2009). Harvest of high-yielding crops plays the most significant role in increasing soil acidity. During growth, crops absorb basic elements such as Ca, Mg, and K to satisfy their nutritional requirements. As crop yields increase, more of these lime-like nutrients are removed from the field. Compared to the leaf and stem portions of the plant, grain contains minute amounts of these basic nutrients. Therefore, harvesting high-yielding forages such as Bermuda grass and alfalfa affects soil acidity more than harvesting grain does (Fageria and Baligar, 2008; Rengel, 2011).

Changes in land use and management practices often modify most soil physical, chemical and biological properties to the extent reflected in agricultural productivity (Gebrekidan and Negassa, 2006). Previous studies indicated that soil properties deteriorate due to the conversion of native forest and range land into cultivated land (Bore and Bedadi, 2015; Lemenih et al., 2005). Such practices result in an increase in bulk density, decline in soil organic matter (SOM) content and CEC (Conant et al., 2003), which in turn reduce the fertility status of a certain soil type. In addition, change in land use associated with deforestation, continuous cultivation, overgrazing, and mineral fertilization can cause significant variations in soil properties and reduction of output (Kang and Juo, 1986; Lemenih et al., 2005).

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SOIL ACIDITY MANAGEMENT 10

Tabl

e 2.

Phy

sicoc

hem

ical

pro

pert

ies o

f som

e ty

pica

l soi

ls in

Eth

iopi

a

Pare

nt m

ater

ial

Soil

type

pHO

M (%)

N (%

)P

(mg

kg-1

)

cmol

(+) k

g-1

Cla

y(%

)

Silt

(%)

Na

KC

aM

g

Trac

hy-b

asal

t and

pyro

clas

ticC

hrom

ic L

uviso

l5.

53.

80.

223.

60.

61.

711

.82.

638

45

Oliv

ine

basa

lt an

dpy

rocl

astic

Eutr

ic N

itiso

l5.

42.

30.

173.

50.

021.

69.

14.

166

28

Wea

ther

ed b

asal

tPe

llic V

ertis

ol6.

82.

30.

149.

90.

62.

740

.09.

064

24

Col

luvi

um a

lluvi

umPe

llic V

ertis

ol, s

odic

pha

se8.

22.

30.

102.

25.

51.

736

.56.

849

25

Volc

anic

ash

Hap

lic P

haeo

zem

6.5

2.6

0.23

11.9

0.8

1.5

20.0

8.3

2341

OM

: Org

anic

mat

ter;

*Olse

n m

etho

d. S

ourc

e: W

olde

ab a

nd M

amo

(199

1)

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Studies have emphasized the negative effect of land use or land cover change on soil properties. For example, the study of Agoumé and Birang (2009) on the impact of land use systems on some physical and chemical soil properties of an Oxisol in the humid forest zone of southern Cameroon showed that land use systems significantly affected the clay, silt and sand fractions. Sand and silt decreased with soil depth, but clay increased. Soil pH, total N, organic carbon, available P, exchangeable cations, exchangeable Al, effective cation exchange capacity and Al saturation significantly differed with the land use systems. Al saturation increased with soil depth, and the top soils presented acidity problems while the sub soils exhibited Al toxicity. Likewise, Chimdi et al. (2012) indicated that a decline in total porosity in the soils of grazing and cultivated land in comparison to soils of forest land was attributed to a reduction in pore size distribution and the magnitude of SOM loss which in turn depends on the intensity of soil management practices. Bore and Bedadi (2015) also reported that the amount of SOM in grazing and cultivated lands has depleted by 42.6 and 76.5%, respectively, compared to the forest soil.

Low buffer capacity from little clay and organic matter

Another source of soil acidity is contact exchange between exchangeable hydrogen on root surfaces and the bases in exchangeable form on soils. Where leaching is limited, microbial production of nitric and sulfuric acids also occurs. The lime requirement of acid soil is related not only to the soil pH but also to the buffer or CEC. The buffering or CEC is related to the amount of clay and organic matter present, the larger the amount, the greater the buffer capacity. Soils with higher buffer capacity (clayey, peats), if acid, have high lime requirement. Coarse textured soils with little or no organic matter will have low buffer capacity and, even if acid, will have low lime requirement. The indiscriminate use of lime on coarse textured soil could lead to over-liming injury (Somani et al., 1996). Therefore, the relationship between pH and percent base saturation is important for soils representative of 1:1 and 2:1 clays, because a much higher base saturation was required to raise the pH to 6 with montmorillonite than with kaolinite. For instance, soils with 2:1 clays (fine, mixed, and thermic Vertic (Hapludults) had to be 80% base saturated to give the same pH as the soils with 1:1 clays (fine, loamy, siliceous thermic Typic Hapludult) at 40% base saturation as determined by the sum of cations, pH 8.2 CEC method (Kamprath and Adams, 2010).

Alumino-silicate minerals

The principal hydrous oxides of the soils are Al and Fe that occur in amorphous, crystalline or colloidal forms as coating on other mineral particles or as inter-layers in clay mineral structures. When the pH of the soil decreases, these oxides get into solution and through stepwise hydrolysis release H+ ions resulting into further acidification (Abebe, 2007; Somani et al., 1996). Soil acidity limits plant growth not only because of the deficiencies of P, Mo, Ca, Mg, etc. but also due to toxicities of Al, Mn and H ions. Toxicities of these elements have been recognized as one of the most common cause of yield reduction in acid soils. Acid soil toxicity is not a single factor but a complex of factors that may affect the plant growth through different physiological and biochemical pathways. Toxicities of Al3+, Mn2+ and low pH (H+ toxicity) are important growth limiting factors associated with acid soil infertility. These toxicity factors may act independently and/or together to affect plant growth (Sanchez, 1977; Somani, 1996).

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5EFFECTS OF SOIL ACIDITY ON NUTRIENT

AVAILABILITY AND CROP YIELDTypes of soil acidity

In acid soils, there are mainly two types of acidity

Active acidity: This occurs because of H+ ion concentration of the soil solution that is attributable to carbonic acid (H2CO3), water-soluble organic acids and hydrolytically acid salts. It can be determined by measuring the pH value of a water suspension or extract from a soil. It bears directly on the development of plants and soil microorganisms.

Exchange acidity: This refers to those H and Al ions adsorbed on soil colloids. There exist an equilibrium between the adsorbed and soil solution ions (i.e. active and exchange acidity), permitting the ready movement from one form to another (Figure 2). Such an equilibrium state is of great practical significance since it provides the basis for the soils buffering capacity or its resistance to change in pH. Since the adsorbed H and Al ions move into the soil solution then its acidity is also referred to as adsorbed or potential or reserve acidity. Reactions of bases (e.g. lime) added to the soil occur first with the active acidity in soil solution. Subsequently, the pool of reserve acidity gradually releases acidity into the active form (Somani, 1996).

Figure 2. Equilibrium relationship between exchange (reserve) and solution (active) acidity, and acid or base inputs.Source: (Somani, 1996)

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Effect of soil acidity on nutrient availability and crop yield

The solubility and availability of important nutrients to plants is closely related to the pH of the soil (Marschner, 2011; Somani, 1996). Soil pH affects the availability of plant nutrients. Effects of high acidity in a soil are shortage of available Ca, P and Mo on the one hand, and excess of soluble Al, Mn and other metallic ions on the other (Agegnehu and Sommer, 2000a; Somani, 1996). Acid soil limits the availability of crucial nutrients such as P, K, Ca and Mg, and affects the movement of soil organisms plants need to stay healthy. If a particular soil is too acidic for plants to grow healthy, it is necessary to raise the pH by applying an alkaline substance.

Soil acidity and associated low nutrient availability is one of the constraints to crop production on acid soils (Bekele and Höfner, 1993; Beyene, 1987; Mamo and Haque, 1991). If a pH of a soil is less than 5.5 phosphate can readily be rendered unavailable to plant roots as it is the most immobile of the major plant nutrients (Agegnehu and Sommer, 2000b; Sanchez, 1977), and yields of crops grown in such soils are very low. In soil pH between 5.5 and 7, P fixation is low and its availability to plants is higher. Toxicity and deficiency of Fe and Mn may be avoided if the soil reaction is held within a soil pH range of 5.5 to 7; this pH range seems to promote the most ready availability of plant nutrients (Somani, 1996). The quantity of P in soil solution needed for optimum growth of crops lies in the range of 0.13 to 1.31 kg P ha-1 as growing crops absorb about 0.44 kg P ha-1 per day (Lawlor, 2004). The labile fraction in the topsoil layer is in the range of 65 to 218 kg P ha-1, which could replenish soil solution P (Lawlor, 2004).

Phosphate sorption (the loss of orthophosphate from soil solution to solid phases) takes place by specific adsorption and precipitation reactions (Sample et al., 1980; Sanchez and Uehara, 1980). Specific adsorption occurs when P anions replace the hydroxyl groups on the surface of Al and Fe oxides and hydrous oxides, while precipitation reaction occurs when insoluble P compounds form and precipitate (Parfitt, 1978). At very low soil pH (≤4.5–5.0), addition of P to soils can result in precipitation of Al and Fe phosphates, whereas at high pH (>6.5) insoluble calcium phosphates can be formed (Haynes, 1984). In many situations, however, specific adsorption reactions are the main regulators of soil solution P concentrations (Parfitt, 1978). Specific adsorption of P is affected by many factors including pH, ionic strength of the background electrolyte and anion competition (Barrow, 1984).

The correct pH depends on the crop being produced as crops differ in their susceptibility to soil acidity. For example, Uchida and Hue (2000) indicated that food and forage legumes, such as beans, peas, and desmodium forage, possess nodules on their roots where bacteria can take N from the air and change it to a form usable by the plant. However, some strains of the bacteria do not thrive at pH values below 6, thus pH 6 or above is best for the legumes that require those particular strains of the bacteria. In contrast, potato scab disease is more prevalent when soil pH is above 5.5; thus, the recommended soil pH for optimum growth of potato is 5.0 to 5.5, although potato plants can grow well at higher pH. Whereas, plants such as azalea and camelia grow well only at pH values below 5.5 and suffer from iron (Fe) and Mn deficiencies at higher pH. The pH of soils for best nutrient availability and crop yields is considered to be between 6.0 and 7.0, which is the most preferred range by common field crops (Duncan, 2002). A summary of crop relation to soil reaction is given in Table 3. Cotton, alfalfa, oats and cabbage do not tolerate acid soils and are considered suitable to neutral soils with a pH range of 7-8. Wheat, barley, maize, clover and beans grow

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well on neutral to mildly acid soils (pH 6-7). Grasses tend to tolerate acidic soils better than legumes, so liming to pH 5.5 may control acidity without limiting production. Legumes, however, need more Ca and perform best between pH 6.5 and 7.5. Among crops tolerant to acid soils are millet, sorghum, sweet potato, potato, tomato, flax, tea, rye, carrot and lupine (Somani, 1996). Poor plant vigor, uneven crop growth, poor nodulation of legumes, stunted root growth, persistence of acid-tolerant weeds, increased incidence of diseases and abnormal leaf colors are major symptoms of increased soil acidity which may lead to reduced yields (Kang and Juo, 1986; Somani, 1996). Increased acidity is likely to lead to poor plant growth and water use efficiency because of nutrient deficiencies and imbalance, and or induced Al and Mn toxicity. High concentration of Al also affects uptake and translocation of nutrients (especially immobilization of P in the roots) (Baquy et al., 2017; Fageria and Baligar, 2008), cell division, respiration, nitrogen mobilization and glucose phosphorylation of plants (Fox, 1979; Haynes and Mokolobate, 2001). 

Table 3. Crop relation to soil reaction (pH)

Crop Optimum pH for best growth Crop Optimum pH for

best growth

Alfalfa 7.0-8.0 Sugar beet 5.8-7.0

Cotton 7.0-8.0 Millets 5.5-7.5

Oats 7.0-8.0 Sorghum 5.5-7.5

Cabbage 6.0-6.5 Sweet potato 4.5-6.5

Wheat 6.0-7.0 Potato 4.5-6.5

Barley 6.0-7.0 Tomato 5.5-7.5

Maize 6.0-7.2 Deciduous fruits 6.5-7.5

Clover 6.0-7.0 Mango 5.0-6.0

Faba bean 6.0-8.0 Papaya 6.0-6.5

Field pea 6.0-7.0 Avocado 5.0-8.0

Chickpea 7.0-8.0 Pineapple 4.5-6.5

Lentil 6.5-8.0 Flax 5.0-7.0

Soybean 6.2-7.0 Tea 4.0-6.0

Beans 5.5-8.0 Carrot 5.5-7.0

Onion 5.8-6.5 Rye 5.0-7.5

Sugarcane 5.0-8.5 Lupin 4.5-6.0

Source: Somani (1996)

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Soil acidity, at pH 5.5 or lower, can inhibit the growth of sensitive plant species, though it has little effect on insensitive species even at pH lower than 4. This pH effect is compounded and often surpassed by Al and Mn toxicity, Ca and Mo deficiency (Baquy et al., 2017; Fox, 1979; Somani, 1996). Roots are commonly the first organs to show injury owing to acid due to Al toxicity; they become stunted, stubbly. Stunted roots have difficulty of getting immobile nutrients, which are frequently deficient in acid soils. The plant’s ability to extract water and nutrients, particularly immobile nutrients such as P, is severely reduced (Fox et al., 1979). Plants are consequently very susceptible to drought and are prone to nutrient deficiencies. The red discolorations often associated with P deficiency are common, micronutrient deficiency symptoms are frequently observed and, due to the direct antagonistic effect of Al on Mg absorption, Mg deficiency symptoms provide a valuable indicator of acidity problems (Marschner, 2011). Exchangeable Al is the dominant cation associated with soil acidity. The damage of the root growth of sensitive crop species is caused when Al in the soil solution exceeds 1 mg kg-1. This often happens when 60% or more of the exchangeable capacity of the soil is occupied by Al. Damage may also be caused by Mn, which becomes very soluble at pH less than 5.5 (Somani, 1996).

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6MANAGEMENT OF SOIL ACIDITY

The management of acid soils should aim at improving the production potential by the addition of amendments to correct the acidity and manipulate the agricultural practices to obtain optimum crop yields. The soil’s acid/alkali balance (measured by pH) of the soil is very important in maintaining optimum availability of soil nutrients and minimizing potential toxicities. For example, at a very low pH Al may become more soluble and can be taken up by roots - becoming toxic, P may become unavailable and Ca levels can be low. At high pH, Fe and other micronutrients (except Mo) are rendered unavailable since they are locked up as insoluble hydroxides and carbonates (Somani, 1996).

The microscopic clay particles and humus in soils are so tiny that they can develop an electrical charge. The tiny clay and humus particles in the soil attract oppositely charged minerals dissolved in water that surrounds them. Clay and humus have a net negative charge, and thus, they attract positively charged minerals, i.e. cations that are dissolved in water. Since soils attract mostly positive charged cations, these are the main concerns. Some of these cations may be essential plant nutrients such as K+, Ca+2, Mg+2, and ammonium (NH4+). There is an abundance of H+ and Al+3 in acid soils. These cations can exchange for one another on the surface of clay and humus, a process known as cation exchange (Brown et al., 2008). The more clay and the more organic matter (humus) in the soil, the more of these cations the soil can hold, and the higher the soil’s CEC. This is why soils high in clay and high in organic matter are generally more fertile than sandy soils; they have a higher CEC (Kamprath and Adams, 2010; Somani et al., 1996).

Liming

Generally, pH 7.0 represents neutrality, and values above this point represent alkaline conditions while values below 7.0 denote acid conditions. Both strongly alkaline and strongly acid conditions are generally detrimental to plant life (Haynes and Naidu, 1998; Rengel, 2011). This is all true, but there are few chemical reactions in nature that occur at neutrality. Liming is the application of calcium- and magnesium-rich materials to soil in various forms, including marl, chalk, limestone, or hydrated lime. It is a desirable practice where soil is highly acidic and multi-cropping involving acid sensitive crops is adopted. Lime, in its most pure form, is made up largely of Ca. Calcium carbonate is a base, and therefore, has a neutralizing effect on acid (Edmeades et al., 2003; Kamprath, 1984). Lime improves base saturation and availability of Ca and Mg. Fixation of P and Mo is reduced by inactivating the reactive constituents. Toxicity arising from excess soluble Al, Fe and Mn is corrected and thereby root growth is promoted and uptake of nutrients is improved. Liming also stimulates microbial activity and enhances N fixation and N mineralization and hence, legumes are highly benefited from liming (Fageria and Baligar, 2008; Pilbeam and Morley, 2007). However, over-liming can considerably reduce the bioavailability of micronutrients, such as Zn, Cu, Fe, Mn and B, which decreases with increasing pH (Fageria and Baligar, 2008). This can produce plant nutrient deficiencies, particularly that of Fe.

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Soil acidity limits or reduces crop production primarily by impairing root growth thereby reducing nutrient and water uptake (Marschner, 2011). Soil acidity converts available soil nutrients into unavailable forms and soils affected by soil acidity are poor in their basic cations, such as Ca, K, Mg, and some micronutrients, which are essential to crop growth and development (Tisdale et al., 1993; Wang et al., 2006). The extent of damage posed by soil acidity varies from place to place depending on several factors, and there are occasions where total crop failure occurs due to soil acidity. Thus, the main effects of liming are increasing the available P through inactivation or precipitation of exchangeable and soluble Al and Fe hydroxides, increase in pH, available P, exchangeable cations and percent base saturation, and enhancing the growth density and length of root hairs for uptake of P (Marschner, 2011).

Liming is a major and effective practice to overcome soil acidity constraints and improve crop production on acid soils. Lime is called the foundation of crop production or ‘‘workhorse’’ in acid soils (Fageria and Baligar, 2008). Lime requirement for crops grown on acid soils is determined by the quality of liming material, status of soil fertility, crop species and varieties, crop management practices, and economic considerations. Soil pH, base saturation, and Al saturation are important acidity indices that are used as a basis for determination of lime rates for reducing crop constraints on acid soils. Besides, crop responses to lime rate are vital tools for making liming recommendations for crops grown on acid soils (Fageria and Baligar, 2008; Rengel, 2011).

Soil acidity can be corrected easily by liming the soil, or adding basic materials to neutralize the acid present. The most economical liming materials and relatively easy to manage are calcitic or dolomitic agricultural limestone (Pilbeam and Morley, 2007; Rengel, 2011). Since these products are natural they are relatively insoluble in water, agricultural limestone must be very finely ground so it can be thoroughly mixed with the soil and allowed to react with soil’s acidity. Calcitic limestone is mostly calcium carbonate (CaCO3). Dolomitic limestone is made from rocks containing a mixture of Ca and Mg carbonates (CaCO3 + MgCO3). Other liming materials which are less frequently used include burned lime (CaO), hydrated lime [Ca(OH)2] and wood ashes (Adams, 1990; Tisdale et al., 1993).

The effectiveness of lime material is expressed by the chemical guarantee as CaCO3, CaO or elemental Ca and by the particle size of the liming materials. The less the particle sizes of the liming material the higher the contact surface of the particle to react with the soil (Somani, 1996). The reaction of lime or calcium carbonate with an acidic soil is described in Figure 3, which shows acidity (H+) on the surface of the soil particles. As lime dissolves in the soil, Ca moves to the surface of soil particles, replacing the acidity. The acidity reacts with the carbonate (CO3) to form carbon dioxide (CO2) and water (H2O); the result is a soil that is less acidic, with a higher pH (Adams, 1990; Somani et al., 1996). The rise in pH of soil is associated with the presence of basic cations (Ca2+) and anions (CO3-2) in lime that are able to exchange H+ from exchange sites to form H2O + CO2. Cations occupy the space left behind by H+ on the exchange leading to the rise in pH (Abebe, 2007; Fageria et al., 2007).

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Figure 3. Neutralizing acidic soil through lime

Amount of lime required

Although harvested crops remove copious lime-like elements each year, the soil pH does not change much from year to year, meaning the soil is buffered, or resistant to change (Somani et al., 1996). The most important source of buffering in an acidic soil is the exchange of the lime-like elements–mostly calcium–attached to the surface of soil particles. As the crop removes these elements from the soil solution, attached elements move from the soil particles to replenish the solution. Over time, reserve elements are depleted enough to cause acidity. When lime is applied, the size of the reservoir or buffering capacity need to be considered. Typically, clay soils have a larger reservoir than sandy ones, which means that they require more lime to achieve a favorable pH (Fageria a nd Baligar, 2008; Rengel, 2011). Attention should be paid to the buffer index or pH on the soil test because it is an indirect estimate of the soil reservoir’s size. Because the lab test involves adding basic material to soils with a pH less than 6.5 and then re-measuring pH, the buffer pH is larger when the reservoir is small. If the buffer pH is 6.8, then it will take 1.2 tons of effective calcium carbonate equivalent (ECCE) of lime to raise the pH to 6.8 and 0.7 ton to increase it to 6.4 (Marschner, 2011; Somani, 1996). Lime requirements are expressed in terms of ECCE, which is established on the basis of two components: the purity of the lime, determined chemically by the calcium carbonate content in the lime material, and the fineness of the lime material, determined by how much it is ground (Ritchey et al., 2016; Somani, 1996). The more calcium carbonate and the finer the material size, the higher the ECCE, because the ECCE of lime is not always 100%, the amount of material required to provide that percentage must be calculated:

ECCE Lime required x 100 = Lime required ECCE% …….. (1)

Methods for estimating lime requirements

The soil lime buffer capacity (BC) is a fundamental property of soil that has many useful applications. It is the measure of the amount of soil acidity that must be neutralized to raise soil pH by one unit. Use of buffer curves to determine the BC of soil groups is an alternative approach to determine the lime requirement (LR) of soil samples. It is simple to use, but less in terms of precision. It is the amount of lime required to

Acid soil + Lime = Netural clay + WaterCarbon dioxideAluminum oxide

H CaCa

Ca

Ca

H

Ca

Ca Ca

Al

H HH

H

Al AlH

H

H20

CO2Al2O3

+

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raise the pH of an acid soil by one unit. BC is the reciprocal of the slope of the buffer curve. Therefore, the LR is determined based on the BC value, target pH, and initial soil pH using the following formula

LR= (Target pH – initial pH of soil sample) x BC ………… (2)

The slope of the curve is determined from the part of the curve that can approximate a straight line. The intercept of the curve on the y-axis is taken as the first point to determine the changes in the pH values per unit of lime applied. The equation can provide a very good estimate of the lime requirements for the range of soil pH classes. The formula can be valid if it is applied within the ranges of soil pH values indicated in the equation. The use of BC method for the determination of lime requirements can be ambiguous for some users. To avoid confusion arising from the subjective nature of BC determination, Table 8 can serve as a guide.

It is to be noted that calcium oxide (CaO) is not usually available for users. Hence, it is necessary to convert the weights of CaO to its equivalent carbonate. Liming materials are normally expressed in terms of calcium carbonate equivalent values (CCE). The CCE value of CaCO3 is considered as a standard (100%). The acid neutralizing value of CaO is normally estimated to be about 130%. The higher neutralizing capacity of CaO, expressed in terms of CCE as 130%, means that in the case of using limestone (CaCO3) in place of CaO, the weights of CaO have to be multiplied by 130%, indicating the need for higher rates of CaCO3 than indicated in Table 9.

There are different materials that are called lime and many can be purchased for this purpose. However, the ground, agricultural limestone is recommended most of the time. This natural rock is ground to a fine powder for spreading. It can be pure calcium limestone (calcium carbonate, CaCO3), or a mixture of calcium carbonate and magnesium carbonate (CaCO3 + MgCO3). The mixture is called dolomite and is usually more desirable because it contains two essential plant nutrients (Ca and Mg) instead of just one. Some of the other products listed here are by-products or industrial products made from limestone (burned lime and hydrated (builders) lime (Table 9). They can all be used to raise the pH of the soil, but some can burn living plants. To be safe, always use ground, agricultural limestone around living plants, and lime only when the soil test shows you need it.

Length of time for lime to work

Agricultural lime is not easily soluble in water as it is a natural product. It requires water to activate the lime reaction, so lime works slowly in dry soil (Adams, 1990; Somani et al., 1996). Even with adequate soil moisture, it may take a year or more for a measurable change in pH. Since neutralization involves a reaction between soil and lime particles, mixing lime with soil increases the efficiency of acidity neutralization (Somani, 1996). Periodical soil testing is necessary when growing high-yielding annual and perennial crops to identify lime deficiency early enough to change the pH with unincorporated broadcast applications. Maintaining a favorable pH is extremely important in a soil fertility management plan (Ritchey et al., 2016). Routine soil testing reveals soil pH levels and provides liming recommendations. Producers often lose forage production by ignoring lime deficiency in soils with acidity problems.

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Short-term effects of lime, i.e., less than one year are likely to be the result of physicochemical effects. On highly-weathered acidic tropical soils, where relatively low lime rates are applied to neutralize exchangeable Al (usually to raise pH-H2O to 5.3 -5.6), precipitation of exchangeable Al as hydroxyl-Al species will be the main factor for improving soil structural condition (Haynes and Naidu, 1998; Somani et al., 1996). Hydroxyl-Al has flocculating and cementing actions. For temperate soils, with a higher initial pH and low levels of exchangeable Al, lime is often applied to raise soil pH-H2O to 6.0 or above. In such situations, the flocculating effect of Ca2+ and the cementing action of lime itself are likely to be the dominant mechanisms in the short-term. In the longer-term, lime-induced increases in crop yields will result in greater input of organic material and a buildup in soil organic matter and soil biological activity both of which favor improved aggregate stability and increased porosity (Haynes and Naidu, 1998).

Frequency of liming

The residual effects of liming are usually expected to last for five to seven years. There is an increase in exchangeable Al with time at all but the high lime rates, possibly because of leaching of bases, uptake of calcium by crop plants, release of H+ ions from organic matter, and residual acidity of nitrogenous fertilizers. Application of 200-500 kg lime ha-1 year-1 has been reported to be adequate to maintain the level of Ca and Mg in the soil under continuous cropping while keeping a check on the release of exchangeable Al (Somani, 1996). Ground limestone when used may have liming action for several years while hydrated lime and quick lime which are usually composed of fine particles and react quickly in the soil may have to be applied more frequently and at lower rates. The best guide for the application of lime is a periodic testing of the soil reaction within the root zone. Inspections at intervals not greater than two to three years are advisable to economize the process of amelioration and to avoid over-liming injury to plants (Rengel, 2011; Somani et al., 1996).

Effect of lime on soil acidity and crop yield

In an attempt to address soil acidity problems, the application of lime has remarkably improved the response of barley and faba bean to P fertilizer application, which is otherwise, immobilized due to P fixation in the central highland Nitisol areas of Ethiopia. Buni (2014) reported that soil pH increased from 5.03 to 6.72 and exchangeable acidity (EA) was significantly reduced due to the application of 3.75 t lime ha-1 on Nitisol with an inherent property of high P fixation in southern Ethiopia. Moreover, liming significantly increased CEC and available P, and decreased available micronutrients except Cu. The highest (33.34 cmol(+) kg-1) and lowest (19.18 cmol(+) kg-1) values of CEC were obtained from the highest lime rate and control treatment, respectively (Table 4).Table 4. Effect of lime on soil chemical properties

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Treatment(lime t ha-1) pH

cmol (+) kg-1 Concentration (mg kg-1)

CEC Al EA1 P Fe Mn Cu Zn

0 5.03d 19.18d 0.68a 0.97a 5.36b 41.96a 70.3a 0.37d 11.67a

1.25 5.64c 25.21c 0.56b 0.75b 6.70a 33.77b 58.4b 0.77b 11.19b

2.50 6.14b 31.49b 0.33c 0.51c 7.04a 25.04b 46.0c 0.99a 9.78c

3.75 6.72a 33.34a 0.24c 0.36c 6.67a 19.01c 34.5d 0.65c 9.75c

LSD (0.05) 0.014 0.738 0.13 0.21 0.94 0.390 4.52 0.059 0.138

CV (%) 3.01 6.24 8.12 6.43 2.04 11.56 14.73 10.11 12.38

1EA: Exchangeable acidity; Source: Buni (2014).

Previous studies indicated that application of different rates of lime and P fertilizer significantly increased barley grain yield in the central highlands of Ethiopia (Beyene, 1987; Desalegn et al., 2017). According to Desalegn et al. (2017), the combined application of 1.65 t lime ha-1 and 30 kg P ha-1 resulted in 133% more grain yields of barley than the control (without P and lime). The highest yield of barley was obtained in the third year after application of lime, implying that the efficiency of lime was more in the subsequent year than the first and second year of its application (Beyene, 1987). Normally, calcium carbonate takes more time to be soluble in water than slaked lime which consists of mostly calcium hydroxide (Somani, 1996). Hillard et al. (1992) indicated that decreasing winter pasture productivity in un-limed Ultisols has been associated with increased soil acidity due to N fertilizer application. Thus, over three harvest years, rye grass yields increased 90-750% and 25-80% at the highest lime and P rates, respectively. In the second year, yield response to applied P was significantly less at the high lime rate, indicating that liming made soil P more plant available. Application of lime and P increased plant tissue P, Ca and Mg concentrations (Agegnehu and Sommer, 2000b; Hillard et al., 1992). Anetor and Akinrinde (2007) reported that un-amended soil remained acidic (pH 4.8), but liming raised pH (6.1-6.6), and resulted in maximum P release (15.1-17.3 mg kg-1) compared to un-amended soil (4.2-7.1 mg P kg-1). The picture in Figure 4 shows the effect of lime on growth of barley in acidic soils.

Figure 4. Growth of barley plants with lime and P, with P alone and without lime in acidic soils of Welmera and Endibir

 

Lime +P P without lime Without lime and P

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According to Agegnehu et al. (2006) the application of lime at the rates of 1, 3 and 5 t ha-1 resulted significantly in linear response with mean faba bean seed yield advantages of 45, 77 and 81% over the control (Figure 4). Desalegn et al. (2017) showed that Application of 0.55, 1.1, 1.65 and 2.2 t lime ha-1 decreased Al3+ by 0.88, 1.11, 1.20 and 1.19 mill equivalents per 100 g of soil, and increased soil pH by 0.48, 0.71, 0.85 and 1.1 units, respectively. Agegnehu et al. (2006) also indicated that soil pH consistently increased from 4.37 to 5.91 as lime rate increased. Conversely, the exchangeable acidity was significantly reduced from 1.32 to 0.12 cmol (+) kg-1 because of lime application. Yield increments showed direct relationship with the soil pH values and inverse relationship with exchangeable acidity, i.e. as the pH increased the yield also increased, but as the exchangeable acidity decreased the yield of faba bean increased and vice versa. Mahler et al. (1988) also found that seed yields of legumes were optimal between soil pH values of 5.7 and 7.2 and yields of pea could be increased by 30% due to lime application to soils with pH values less than 5.4. The picture in Figure 5 shows the effect of lime on growth of faba bean in acidic soils.

Figure 4. Faba bean mean seed yield as influenced by the application of lime in the form of calcium carbonate at Holetta, 998-2000LSD at 5% = 192, Error bars represent ±1 SE. Source: Agegnehu et al. (2006)

Figure 5. The growth of faba bean under limed and un-limed condition on acidic soils Welmera Woreda

Soil acidity and deficiency of nutrients, particularly P and K are the key soil related constraints that account for low yield of crops in Chencha and Hagereselam areas of southern Ethiopia. The soil pH at the testing site of Chencha ranged from 4.8-5.0 and the concentrations of P and K were 3.2 and 11.2 mg kg-1, respectively, which are very low. Application of NP and NK fertilizers without lime did not increase potato tuber yield, but application of PK fertilizer without lime significantly increased the tuber yield at both locations (Haile and Boke, 2009). Addition of PK fertilizer alone increased tuber yield by 267,

c

b

a a

300

600

900

1200

1500

1800

0 1 3 5

Faba

bea

n se

ed yi

eld

(kg h

a-1)

Lime rate (t ha-1)

Faba bean with lime Faba bean without lime

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SOIL ACIDITY MANAGEMENT 23

151 and 198% over the untreated control, fertilizer NP and NK treatments, respectivelly at Chencha; and 278, 46 and 61%, respectivelly at Hagereselam. This implys that K is more effective with P than N. Likewise (Junquan et al., 2007), reported that K had no effect on pasture when applied without N, but had a significant effect on the yield of white clover when applied with P fertilizer. The authors suggested that this is probably due to increased retention of K when applied along with P in acid tropical soils because of precipitation of Al as Al phosphate. Li et al. (2015) showed that significantly higher response of potato was obtained when K fertilizer was applied with balanced N and P fertilizer. Other studies also indicated that the application of K fertilizer on acidic soils increased yields of potato in Pakistan (Khandakhar et al., 2004) and Nepal (Adhikari and Karki, 2006). Significantly, higher yield of potato was obtained at Chencha (20.5 t ha-1) than at Hagereselam (13.8 t ha-1) in 2007. The tuber yield at Chencha was 42-279% higher than at Hagereselam (Figure 5). Haile and Boke (2009) indicated that application of lime alone did not significantly improve potato tuber yield. This implies that Chencha soil is better in fertility and more responsive to the treatments than Hagereselam soil, which is low in soil pH, nutrient content and yield.

Application of lime improves the yield of crops if an acidic soil has essential nutrients rendered unavailable to crops due to low pH. However, if the soils are already depleted of nutrients, limited response is expected to lime application only (Marschner, 2011). In this study, however, application of NPK + lime resulted in the highest potato tuber yield of 30.67 at Chencha with yield increments of 332 and 73% over NP and NPK fertilizer treatments alone, respectively. While at Hagereselam, the same treatment resulted in the highest tuber yield of 10.03 t ha-1 with yield increments of 82 and 59% over NP and NPK fertilizer treatments alone, respectively(Figure 5). These marked increases in the yield of potato is due to K application along with NP, suggesting that balanced appliction of NPK is more efficient than applying NP alone in K deficient soils. Studies also indicated that the combined of application NPK produced significantly superior maize yield compred to PK, NK or NP alone (Ayalew, 2007; Saıdou et al., 2003). Therefore, to enhance crop production in acididic soils application of lime alone cannot be the sustainable solution without considering the principle of balanced application of nutrients.

Figure 5. Lime and NPK fertilizers effects on tuber yield of Irish potato at Chencha and Hagereselam, southern Ethiopia, 2007-2009. Data synthesized from Haile and Boke (2009). Error bars represent ±1 SE. Note: Units of fertilizers and lime are in kg ha-1 and t ha-1, respectively.

0.005.00

10.0015.0020.0025.0030.0035.00

Potat

o tub

er yi

eld (t

ha-1

)

Chencha Hagereselam

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SOIL ACIDITY MANAGEMENT 24

Integrated soil fertility management (ISFM)

Integrated soil fertility management (ISFM) is one of the approaches to manage and improve soil health and fertility status (Agegnehu and Amede, 2017; Fageria and Baligar, 1997). ISFM is one of the components of the management of acid soils. Farmyard manure (FYM) and crop residues are among organic plant nutrient sources, which could ameliorate the physical and chemical properties of soils. For example, Lal (2009) indicated that returning crop residues to soil as amendments is essential for recycling plant nutrients (20–60 kg of N, P, K, Ca per Mg of crop residues) amounting to 118 million Mg of N, P, K in residues produced annually in the world (83.5% of world’s fertilizer consumption). In acid soils, where P fixation is a problem application of FYM releases a range of organic acids that can form stable complexes with Al and Fe thereby blocking the P retention sites, and as a result, the availability and use efficiency of P is improved (Agegnehu and Amede, 2017; Prasad and Power, 1997; Sharma et al., 1990). The positive effects of manure on crop yields have been explained on the basis of cation exchange between root surfaces and soil colloids (Sharma et al., 1990; Walker et al., 2004).

The addition of organic fertilizers to acid soils has been effective in reducing phytotoxic levels of Al resulting in yield increases. The major mechanisms responsible for these improvements are thought to be the formation of organo-Al complexes that render the Al less toxic or direct neutralization of Al from the increase in pH caused by the organic matter. The possible alternative of using organic sources such as crop residues, manures, compost and biochar are substitutes for lime (Agegnehu and Amede, 2017; Sharma et al., 1990). The authors demonstrated that organic sources raises pH and precipitate Al in direct proportion to its basic cation or ash alkalinity with a correction for the acidity produced during the oxidation of the N in the material. For instance, Cornelissen et al. (2018) found that cacao shell biochar exhibited a higher pH (9.8 vs. 8.4), CEC (197 vs. 20 cmol kg-1) and acid neutralizing capacity (217 vs. 45 cmol kg-1) and thus had a greater liming potential than rice husk biochar. Haile and Boke (2009) also reported that the combined application of NP fertilizer and FYM on acid soil of Chencha, southern Ethiopia significantly increased potato tuber yield and some soil chemical properties relative to application of NP alone.

In tropical regions, crop yields generally decrease with time, partly due to a decline in the levels of exchangeable bases linked to acidification of the upper layers of the soil. The management of acid soils through integrated soil fertility and plant nutrient management not only improve the yields of crops but also the chemical properties of soils. Regular applications of organic residues can induce a long-term increase in SOM and nutrient content. According to Haynes and Mokolobate (2001), complexation of Al by the newly-formed organic matter tends to reduce the concentrations of exchangeable and soluble Al. As organic residues decompose, P is released and can be adsorbed to oxide surfaces. This can reduce the extent of adsorption of subsequently added P thus increasing P availability. The practical implication of these processes is that organic residues may be used as a strategic tool to reduce the rates of lime and fertilizer P required for optimum crop production on acidic, P-fixing soils. Agegnehu and Bekele (2005b) found that the application of 4 and 8 t FYM ha-1 with 26 kg P ha-1 on acid Nitisols of Holetta, Ethiopia, increased faba bean seed yield by 97 and 104%, respectively, compared to the control (Table 5). The same rates increased soil pH from 4.5-5.0, N from 0.09-0.15%, P from 4.2-6.0 mg kg-1, and K, Ca and Mg from 1.25-1.45, 4.77-7.29 and 0.83-1.69 cmol (+) kg-1, respectively.

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SOIL ACIDITY MANAGEMENT 25

Table 5. Interaction effects of FYM by phosphorus on faba bean seed yield at Holetta, 2002-2003

Phosphorus(kg ha-1)

Farmyard manure (t ha-1)

0 4 80 991 1395 1981

13 1412 1701 194226 1317 1954 201939 1467 1958 221052 1573 2007 2191SE 58.68

Source: Getachew et al. (2005)

Similar studies showed that the residual effects of manure and compost applications significantly increased electrical conductivity (EC), pH levels, plant-available P and NO3-N concentrations (Eghball et al., 2004; Walker et al., 2004). In this regard, Sharma et al. (1990) reported the use of manure might have made the soil more porous and pulverized, so as to allow better root growth and development, thereby resulting in higher root CEC. Insufficient fertilization of one nutrient causes the loss or the imbalance of other essential nutrients. For example, Poss and Saragoni (1992) reported that an insufficient application of K fertilizer increases leaching losses of Ca, Mg and N. Therefore, aapplication of organic residues not only increase crop yield through the release of nutrients but also improve the physical, biological and chemical properties of soils.

Management of acid soils using acid tolerant crop varieties

Over the past decade, several researchers around the world have focused their efforts on identifying and characterizing the mechanisms employed by crop plants that enable them to tolerate Al toxic levels in acid soils. The two distinct classes of Al tolerance mechanisms are those that operate to exclude Al from the root apex and those that allow the plant to tolerate Al accumulation in the root and shoot symplasm (Kochian et al., 2004; Ma et al., 2001). Although there has been considerable speculation about a number of different Al tolerance mechanisms, most of the experimental evidence has focused on root Al exclusion based on Al-activated organic acid (OA) exudation from the root apex. Evidence is also increasing for a second tolerance mechanism based on internal detoxification of symplastic Al via complexation with organic ligands, again primarily OAs (Barcelo and Poschenrieder, 2002; Garvin and Carver, 2003; Poschenrieder et al., 2008).

A substantial number of plant species of economic importance are generally regarded as tolerant to acid soil conditions. Many of them have their center of origin in acid soil regions, suggesting that adaptation to soil constraints is part of the evolutionary process (Somani, 1996). Although the species as a whole does not tolerate, some varieties of certain species also possess acid soil tolerance. Quantitative assessments of plant tolerance to acid soil stresses include tolerance to high levels of Al or Mn, and to deficiencies of Ca, Mg, P, etc. Species and genotypes within a species have been reported to have considerable variation in

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SOIL ACIDITY MANAGEMENT 26

their tolerance to Al and Mn (Kochian et al., 2004; Somani, 1996). The selection of varieties or species that perform well at high Al saturation levels and thus need only a fraction of the normal lime requirement is of great practical importance (Table 6). Table 6. Crops and pasture species suitable for acid soils with minimum lime requirements

Lime (t ha-1)

Al satura-tion (%)

pH Crops (using tolerant varieties)

0.25 to 0.5 68 to 75 4.5 to 4.7

Upland rice, cassava, mango,citrus, pineapple, sugarcane

Desmodium

0.5 to 1.0 45 to 58 4.7 to 5.0 Cowpeas, plantains

1.0 to 2.0 31 to 45 5.0 to 5.3 Corn, black beans

Source: (Somani, 1996)

In the highlands of Ethiopia, barley is mainly grown on Nitisols, where soil pH is low. This means that barley has been already adapted to acid soil conditions. With this understanding five released barley varieties were evaluated under limed and unlimed condition on acidic soils at Endibir. Barley varieties (HB-42 and Dimtu) performed well under limed condition, i.e. yield increments of 366 and 327%, respectively over the corresponding yields of the same barley varieties under unlimed condition were recorded. In contrast, barley varieties (HB-1307 and Ardu) performed better under unlimed condition, i.e. lower yields of 48 and 49% compared to the corresponding yields of the same barley varieties achieved under limed condition (Table 7).

Table 7. Performance of five released barley varieties and one local check under limed and un-limed conditions at Endibir, 2009

Variety Grain yield(kg ha-1)

Yield increment(%)

Limed unlimedHB-42 1752 376 366Shegie 1690 982 72local 1933 1189 63

HB-1307 2162 1459 48Ardu 2020 1355 49

Dimitu 1818 426 327LSD (0.05) 704 1055

Source: HARC (2010)

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SOIL ACIDITY MANAGEMENT 27

Management of sub-soil acidity

Although top soil acidity is the major and extensive problem, amelioration of subsoil acidity is an important agronomic objective in many areas of the world (Farina et al., 2000; Shainberg et al., 1989). It is complicated by differences in the efficacy of lime and gypsum across the diverse soil environments where the problem occurs. The most promising strategies available for achieving this objective include surface incorporation of gypsum (Shainberg et al., 1989); plow-sole incorporation of lime in quantities sufficient to ensure downward movement of the alkaline component (Helyar, 1991); and subsoil incorporation of lime using deep moldboard plows (Farina and Channon, 1988).

Choice of the best approach to adopt is dictated by economic considerations and is also strongly soil dependent. For example, some soils, particularly those that are sandy or have been acidified by anthropogenic activities, may not be responsive to gypsum (Horsnell, 1985), while deep tillage is undesirable on soils with dense sub-soils (Coventry, 1991). Evidence also suggests that gypsum application rates used with such success in the tropical savannas of Brazil (Ritchey et al., 1995) have few beneficial effects on less intensely weathered, but equally acidic Oxisols and Ultisols of South Africa (Farina, 1997). Likewise, the quantities of lime required to elevate topsoil pH levels sufficiently to promote downward movement of alkalinity in intensely weathered soils of the humid and sub-humid tropics (McKenzie et al., 1988) are much less than those needed on soils of similar acidity in less weathered environments (Farina and Channon, 1988). In the latter environments, soils equally acidic to their textural and morphological counterparts in the moist tropics usually contain greater amounts of exchangeable Al, as well as substantial quantities of potentially active Al associated with mixed layer clay mineralogy. This reserve acidity constitutes an important component of lime buffer capacity in the pH-H2O range 4 to 6 (Kamprath, 1984) and it is conceivable that replenishment of Al3+ from initially non-exchangeable sources is also responsible for the very high gypsum requirements recorded on some such soils (Farina, 1997).

Studies showed the ineffectiveness of attempting to ameliorate deep-seated soil acidity with lime and also indicated that the greater quantities of exchangeable and non-exchangeable Al associated with mixed-layer clay mineralogy (Farina et al., 2000) similarly reduce the efficacy of gypsum. The slow movement of gypsum also shows the need for long-term research. Benefits of gypsum were evident only in the sixth season in the 0.60-0.75 m horizon, and acidity in the 0.75-0.90 m horizon actually increased significantly. Farina et al. (2000) indicated that acid-subsoil amelioration in soils with Al-hydroxy–interlayer minerals requires greater quantities of gypsum than soils that are dominated by kaolinitic minerals.

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SOIL ACIDITY MANAGEMENT 28

Tabl

e 8.

Est

imat

ion

of li

me

requ

irem

ents

for d

iffer

ent s

oil p

H ra

nges

usin

g BC

met

hod

pH ra

nges

us

ed in

the

curv

e

Cur

ve

slop

es

BC

(g

/100

so

il)

BC

(k

g ha

-1)

Rem

ark

or re

com

men

datio

n on

the

use

of B

C v

alue

s

Exam

ples

of l

ime

rate

s to

rais

e a

give

n so

il pH

to ta

rget

pH

pH ra

nge

Lim

e ra

te

(kg

ha-1

)In

itial

Targ

et

Estim

atio

n of

BC

val

ues a

nd li

me

rate

s (kg

/ha)

for s

oils

with

pH

bet

wee

n 5.

0 an

d 5.

6 to

rais

e th

e pH

bet

wee

n 6.

0 an

d 6.

5

5.17

-6.1

231

.61

0.03

1664

4Fo

r soi

ls w

ith p

H 5

.0-5

.65.

26.

053

0

5.17

-6.4

24.8

70.

0402

844

Acc

epta

ble,

but

less

eco

nom

ical

for o

ne ti

me

use

5.2

6.4

1010

Estim

atio

n of

BC

val

ues a

nd li

me

rate

s (kg

ha-

1) fo

r soi

ls w

ith p

H b

etw

een

4.5

and

5.0

to ra

ise

the

pH b

etw

een

6.0

and

6.5

4.65

-6.0

11.2

10.

0892

1873

For s

oils

abo

ve p

H 4

.64.

86.

022

50

4.65

-6.3

08.

260.

1211

2544

Expe

nsiv

e4.

86.

338

20

4.63

-5.6

112

.24

0.08

1717

16C

heap

er fo

r one

tim

e us

e, m

aybe

with

insi

gnifi

cant

yie

ld

redu

ctio

nTh

e ra

te is

not

reco

mm

ende

d fo

r spl

it or

loca

lized

app

licat

ion.

4.8

5.6

1370

Estim

atio

n of

BC

val

ues a

nd li

me

rate

s (kg

ha-

1) fo

r soi

ls w

ith p

H b

etw

een

3.8

and

4.5

to ra

ise

the

pH b

etw

een

6.0

and

6.5

4.27

-5.2

416

.24

0.06

1612

93C

heap

for o

ne ti

me

use;

per

haps

, with

som

e le

vel o

f yie

ld

pena

lty4.

275.

2412

54

4.27

-5.6

113

.48

0.07

4215

57A

ccep

tabl

e fo

r one

tim

e us

e; p

erha

ps w

ith in

sign

ifica

nt y

ield

re

duct

ion

4.27

5.6

2070

4.27

-5.8

411

.23

0.08

9118

71M

oder

atel

y ac

cept

able

4.27

5.8

2940

4.27

-6.0

39.

270.

1079

2265

Expe

nsiv

e to

brin

g th

e pH

from

bel

ow 4

.3 to

6.0

4.27

6.0

3918

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SOIL ACIDITY MANAGEMENT 29

Table 9. Common liming materials and their calcium carbonate equivalent

Name Chemical formula Equivalent (%CaCO3)

Calcitic limestone CaCO3 90-100

Dolomitic limestone CaCO3+MgCO3 95-110

Oxide/burned lime CaO 150-175

Hydrated lime Ca(OH)2 120-135

Ground shells CaCO3 80-95

Basic slag CaSiO3 50-80

Wood ashes Oxides and hydroxides 30-70

Source: Michael (2000)

To be most effective, lime should be mixed with the soil well ahead of planting. Putting lime on the surface of a lawn or garden will prevent it from getting more acid, but it will not change the pH beyond an inch or so deep. The lime must react with the hydrogen cations attached to the surface of the clay and humus in the soil. Ca and/or Mg replace the hydrogen on the clay. The hydrogen is then converted back into water and the carbonate becomes carbon dioxide, which goes into the air as a gas. The same thing happens when an acid stomach is treated with a Tums. It should always be remembered that when soils are limed plants should be sufficiently fertilized.

Prediction models to determine LR for acid soils A number of field trials were conducted on acidic soils in different parts of the country. The mathematical models used to calculate LR were as follows

LR,CaCO3(kg/ha)= cmol EA / kg soil x 0.15m x 104m2 x B.D(mg / m3) x 1000 …………… (3)2000

LR,CaCO3(kg/ha)= cmol EA / kg soil x 0.15m x 104m2 x B.D(mg / m3) x 1000 x 1.5……… (4)2000

Where LR = Lime requirement (kg ha-1); CaCO3 = Calcium carbonate; EA = Exchangeable acidity; B.D. = Bulk density of soil

The first and second calculations were done with the assumption that 1.0 and 1.5 mole of EA would be neutralized by the respective equivalent mole of CaCO3. Based on the first formula, experimental results on acidic soils of Lemu Bilbilo in Arsi zone showed that application of lime at the rate of 192 kg ha-1 along with the recommended NP rate resulted in the highest yield of bread wheat (EAAPP, 2015). Similar field trials were conducted in three Weredas (Gozamen, Sekela and Banja) of Amhara region on lime rate and application methods. Results indicated that localized application of lime could reduce the full

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SOIL ACIDITY MANAGEMENT 30

recommended dose using the exchangeable acidity method to a very low level that can be well accepted by resource poor farmers without yield reduction. For example, 25%, 20% and 12.5% of the full dose of 3763 kg lime ha-1 resulted in higher yields compared to the treatments which consisted of 1.0 and 1.5 times the EA with broadcast application in Gozamen Wereda. This means that farmers can apply lime rates within the ranges of 470-940 kg ha-1 in this Wereda and similar areas. In contrast, since soil acidity is severe in Sekela Wereda, lime rates could be within the ranges of 670–1340 kg ha-1 using localized method of application, and the same rates can be applied in Banja area.

It is vital to develop prediction tools and models for the determination of lime requirements of different acid soils based on measurements of soil characteristics and then determination of BC. Soil physicochemical properties, such as soil particle size distribution, minerals, pH, organic matter, bulk density, and exchangeable acidity are required to characterize soils. The constant values for the models cannot practically be applied for prediction of LR for any soils based on pH values of initial soil samples and predetermined target pH values. For instance, in this case the initial pH values of the soils of interest could be used as constant values in the prediction process. Thus, the constant values can be replaced by initial soil pH values in the models for the soils of interest, generally designed as pHi. The following equations (1-3) are the LR predictor models developed by linear regression.

Equation1 for pH 3.8 – 4.5: phf = pHi + 22.836 x LR – 109.968 x LR2 + 209.63 x LR1

Equation1 for pH 4.6 – 5.2: phf = pHi + 26.35 x LR – 132.52 x LR2 + 224.44 x LR1

Equation1 for pH 5.2 – 5.8: phf = pHi + 33.49 x LR – 263.43 x LR2 + 720 x LR1

pHi and pHf stand for initial and target soil pH values, respectively. For example, the target soil pH value for wheat is 6.0. Generally, raising soil pH values by 0.5 above the target values is recommended, but considering the cost of liming, rising above 6.0 could be expensive.

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7EXPERIENCE FROM BRAZIL

The Brazil Cerrado experience provides an important lesson in this perspective. Brazil took the approach of launching a large-scale, well planned, focused and integrated acid soil reclamation program, and was able to convert their low productive Cerrado region into a bread basket that has made the country one of the top five agricultural producers in the world (Klink, 2014). It has been estimated that from the 207 million ha, 136 million ha, which is equivalent to two-thirds of the area, could be incorporated into the productive system (Thomas, 1995). The Brazilian initiative brought together government resources, the EMBRAPA research institute, and international technical and financial aid to carry out an intensive rehabilitation initiative. As a result, with the use of appropriate technology and inputs, infrastructure and policy support, Brazil has been able to develop more than 60 million ha of the Cerrado with crops and improved pasture (Klink, 2014). Different initiatives were taken in the development of agricultural production in the Cerrado.

• EMBRAPA, the national research institute was created shortly before the development of the Cerrado. More importantly, the Cerrado Agricultural Research Center (CPAC), also referred to as EMBRAPA Cerrado, was established to specifically address the research needs of the Cerrado region.

• The country established a good transportation network serving the Cerrado region to provide good access to inputs, machinery and services for the region as well as to markets outside the region.

• EMBRAPA developed effective technical packages suitable to agricultural production in the Cerrado – the use of lime for soil acidity reduction; management of macro- and micronutrients; organic matter management; minimum- and conservation tillage systems; development of crop and pasture varieties suited to the Cerrado; and development of crop-livestock systems

• Most importantly, the government developed a comprehensive finance and credit system to address not only credit requirements for input procurement, but also financing for investment in production infrastructure. To achieve this, it created the national program for strengthening family agriculture (PRONAF) with a focus on family farms (Guanziroli and Basco, 2014). Its efforts on this front were such that, in 2010 for example, over 3.5 million family farmers were accredited to take credit through PRONAF (Antoniazzi et al., 2013). Brazil in fact had a number of different systems and policies in place to ensure the success of the family farm, ranging from finance and credit to government procurement programs and production insurance that were aimed to address the needs of people across the production chain (Antoniazzi et al., 2013).

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One of the characteristics of the development of the Cerrado has been that Brazil not only established both technical and institutional components to its development, but also continually monitored progress and revised and updated its interventions with lessons gained (Klink, 2014). A similar approach is needed in Ethiopia whereby lessons can be learned regarding bottlenecks that have significantly curtailed the treatment and effective management of the country’s acid soils. Research is necessary to give technical support for the development of an ecologically sound and economically viable management of acid soils. The research results will provide information for farmers’ decisions on sustainable land management; develop technologies which increase the productivity of crop-livestock systems; promote the improvement of degraded lands; and monitor changes in soils due to agricultural activities. This is expected to promote a technology transfer through the validation and adaptation of research results. A broad diagnosis was made of the major limitations for agricultural improvement, identifying the priority problems (‘the big six’) as a basis for establishing the research program

• a low knowledge of the natural resources;• the irregular distribution of rainy and dry spells• the low fertility of the soils• soil degradation;• the occurrence of pests and diseases; and• inefficient production systems.

The research projects have been organized in three programs: natural resource evaluation, soil and water management, and production systems. The following are major achievements of these programs

Natural resource evaluation

• the characterization of the resources: soil, water, vegetation, and source of nutrients (limestone, phosphate rocks, etc.) at the regional and local level;

• the development of remote sensing techniques and geographical information system for environmental characterization, land use, and agro-ecological zoning;

• the characterization of rainfall and dry spell distribution; • the characterization of resources in watersheds/landscapes;• the characterization of the potential of native species for food and fiber; and • the creation of a germplasm bank of native vegetation.

Soil and water management

Soil fertility: determination of the critical level, the residual effects and the source of nutrients; cycle of macro- and micronutrients for the principal crops; recommendations for the rational use of limestone and phosphate rocks for soil amendment.

Soil microbiology: development of methodology of application and selection of Rhyzobium strains for legumes cultivated in acid soils (this technology represents an economy in million dollars in imported N fertilizer).

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SOIL ACIDITY MANAGEMENT 33

Soil management and conservation: technologies to determine soil, water and nutrient losses under different management systems; recommendations for conservation practices; the effect of green manure on the chemical, physical and biological properties of soils; studies of soil organic matter dynamics (degradation, conservation) related to changes in soil properties.

Dry spells: the development of technologies to minimize the effect of dry spells, such as varieties resistant to drought, deep incorporation of lime, mulching, correction of acidity of deeper layers by gypsum, and the elimination of compacted layers.

Irrigation: technologies to determine the necessity of water, the definition of irrigation momentum, nutritional requirements, irrigation engineers, and the drainage of wetlands.

Mechanization: development of equipment such as a forage–planting machine, a garlic-planting machine, plough/planting machines, and harvesting machines.

Production system

The main considerations under this heading are

• varieties of food legumes, wheat, barley, root crops, highland fruits and trees;• management of dairy- and beef cattle;• legumes for supplementing feed of cattle in native pasture;• techniques for the recovery of degraded pastures;• characterization, management and control of insect pests, diseases and weeds of major crops; and• production systems for small farmers, and the orientation for organizing community associations.

Table 10 demonstrates priorities for basic, strategic, national and local research in soil, and nutrient management, which have been practiced in Brazil and other similar countries to tackle issues related to soil acidity and nutrient management.

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Table 10. Example of priorities for basic, strategic, national and local research in soil, and nutrient management

Types of research

Theme Basic Strategic National Local

Soil restoration

Establishing critical limits

Developing pedo-transfer functions for specific ecosystems

Identifying cause-effect relationships

Validating and adapting restorative measures, identifying policy issues

Nutrient management

Processes of nutrient cycling, modeling nutrient flow

Ecological research on nutrient dynamics, mechanisms of nutrient cycling

Mass balance of specific nutrient under different management systems, bio-logical nutrient management

Cultural practices of nutrient management, soil-specific response functions, indigenous knowledge

Erosion management

Evaluating soil erosion processes, standardizing methods of assessing soil erosion

On-site and off-site effects, ecological processes and soil erosion

Cultural practices and soil erosion, soil erosion-crop productivity relations

Social and cultural factors, on-farm research and demonstrations, policy issues

Soil acidity management

Basic processes and principles, role of Al and Mn, charge properties, clay minerals and soil acidity

Acidity characteristics of benchmark soils, genotype-soil interaction

Cultural practices for acidity management, seasonal changes

Lime requirements for soil types and cropping systems.

Source: Lal (1995)

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SOIL ACIDITY MANAGEMENT 35

8POLICY CONSIDERATIONS

Ethiopia has taken policy decisions to address the problem of soil acidity in the country. Some of these actions, including providing lime at subsidized prices, are justified because of market failure arguments. However, it is essential to examine whether these decisions are leading to the most efficient pathways of achieving the policy goal, i.e., amending the country’s acidic soils in a cost-effective and welfare maximizing way. The country has planned to rehabilitate 226,000 ha of agricultural land affected by soil acidity until 2021. Three broad aspects of cost-effectiveness analysis should be considered:

• benefits of correcting acid soils with lime, • value chain efficiency (effectiveness of delivering lime to farmers), and • responses of farmers to the intervention (willingness to pay and adopt the lime technology).

The following sections present results of an assessment on benefits of amending acid soils and the efficiency of the lime value chain.

Benefits of amending acid soils with lime

Key development goals set for the agricultural sector include attaining food sovereignty - particularly in basic agricultural commodities, supplying agricultural raw materials for the expanding domestic agro-industry and increasing agricultural exports to generate foreign exchange. Although Ethiopia has vast agricultural land in the lowlands, the necessary infrastructures such as irrigation have not yet been developed. Increased agricultural productivity, therefore, at least in the short run has to come from the already cultivated lands that are characterized by high soil acidity and declining soil fertility due to excessive removal of nutrients by leaching and low input cropping systems (Regassa and Agegnehu, 2011). Consequently, crop yields are not only depressed but are declining over time due primarily to worsening soil acidity. Thus, most soils in the highlands require improved management practices to address soil acidity problems as well as declining soil fertility.

Agricultural research and development efforts in Ethiopia, as well as elsewhere in the world, indicated that a breakthrough in agricultural development in acid soil areas could be achieved by using integrated soil fertility management practices involving agricultural lime. Liming is a soil management practice essential for correcting low pH and Al toxicity with a dramatic effect on crop productivity. Various studies indicated that liming increases soil pH and availability of P, Mo and N, and eliminates Al and Mn toxicity (Abebe, 2007; Ayalew, 2007; Yamada, 2005). Lime, used in conjunction with other complementary agricultural practices/inputs, offers substantial yield improvements. As indicated in Table 11, productivity improvements ranging from 50% to over 100% in wheat, barley, tef, soybean and maize are reported in Ethiopia under

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SOIL ACIDITY MANAGEMENT 36

moderate to severe acid soil conditions (Abewa et al., 2014; Asrat et al., 2014; Ayalew, 2007; Chimdi et al., 2013; Kidanemariam et al., 2013). In most cases, P, K and N fertilizers should be applied together with lime and other improved management practices to achieve substantial yield increases. Moreover, a single application of lime has between five to seven years of productivity benefits. Evidence, therefore, suggests that agricultural programs, with the aim of improving agricultural productivity, should ensure adequate quantities of lime produced and made available to farmers in the most efficient way possible.

Although the government has planned to expand the production, distribution and adoption of agricultural lime by smallholder farmers, lime use for reducing soil acidity is very low in Ethiopia, which was limited to about 5100 ha as of 2015 production year. However, efforts in expanding lime use are expected to raise agricultural production and will have several benefits to the national economy. First, the increase in net farm income would affect the local, regional and even national business activity. Second, enhanced agricultural production would mean availability of supplies of agricultural products for domestic consumption and agro-industries. Third, increased supplies of agricultural products, such as soybean and faba bean would likely improve the export earnings of the country. Finally yet importantly, increased agricultural production would mean less import of basic agricultural commodities such as wheat, affecting not only food security but also save hard-earned foreign exchange.

At the farm level, the economic rate at which farmers apply lime depends on net farm returns to lime application. Several factors need to be considered to evaluate the costs and benefits of lime application at the household level. These include expected yield increases, prices per unit of lime, transportation and application stages, as well as the expected number of years of enhanced productivity. All of these factors affect net farm returns of lime use. A rough calculation of net farm returns to lime application based on experimental results suggest that application of lime is generally profitable particularly when used in moderate amounts ranging from 2.0 to 2.2 t ha-1 in conjunction with other improved agricultural practices (use of inorganic and organic fertilizers, high yielding varieties and associated better agronomic practices). Accordingly, considering wheat and productivity improvements from 0.9 t ha-1 to 1.6 t ha-1 due to lime use only, estimated gross and net returns are estimated at birr 7524 and birr 2324 ha-1, respectively, from an average application of 2.2 t lime ha-1 (Table 12).

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Tabl

e 11

. Effe

ct o

f lim

e an

d ot

her s

oil f

ertil

ity m

anag

emen

t on

crop

yie

ld a

nd so

il pr

oper

ties

Cro

pTr

eatm

ent

Yie

ldEf

fect

on

soil

prop

ertie

s and

nut

rient

upt

ake

Sour

ceM

anur

e(t

ha-1

)Li

me

(t ha

-1)

(t ha

-1)

% in

crea

se o

ver

cont

rol

Whe

at0-

5.0

0.0-

2.20

0.90

-2.6

994

-199

Asr

at e

t al.

(201

4)

Whe

at0-

102.

44-4

.27

34-7

5Li

min

g im

prov

ed so

il pH

and

pla

nt P

upt

ake.

Bor

e an

d B

edad

i (20

16)

N/P

/K (k

g ha

-1)

Lim

e (t

ha-1

)Y

ield

(t

ha-1

)%

incr

ease

ove

r co

ntro

l

Tef

0-46

/0-

26/0

0.00

-2.0

00.

82-2

.88

99-2

52Li

min

g in

crea

sed

soil

pH fr

om 5

.38

to 6

.17

and

CEC

from

14.

8-20

.7A

bew

a et

al.

(201

4)

Soyb

ean

18/2

0/0

0.00

-3.7

5In

crea

sed

soil

pH fr

om 5

.03-

6.72

, and

redu

ced

Al3

+ fr

om 0

.68-

0.36

cm

ol

kg-1

Bun

i (20

14)

Soyb

ean

18/2

0/0

0.00

-2.6

01.

58-2

.31

28.9

-45.

9In

crea

sed

nodu

le d

ry w

eigh

t by

100%

.B

eker

e et

al.

(201

3)

Bar

ley

50/0

-30/

00.

00-2

.20

2.54

-4.5

652

-81

Lim

e re

duce

d A

l3+

by 0

.88-

1.19

meq

100

g-1

soil,

and

rais

ed so

il pH

by

0.48

-1.1

uni

ts.

Des

aleg

n et

al.

(201

7)

Bar

ley

145/

00/0

00.

00-7

.00

2.52

-4.2

415

-68

Lim

e in

crea

sed

pH in

the

surf

ace

15 c

m, b

ut re

duce

d A

l3+

only

in th

e 0-

5-cm

laye

r.Ta

bith

a et

al.

(200

8)

Bar

ley

41/2

0/0

0-4.

51.

28-1

.83

4.0-

41.2

Lim

ing

incr

ease

d so

il pH

from

4.5

3-5.

61 a

nd re

duce

d EA

from

2.2

-0.2

3 cm

ol k

g-1

Bey

ene

(198

7)

Oat

-0.

0-2.

00.

96-1

.48

5-54

Lim

ing

redu

ced

the

H+

and

Al3

+ co

nten

ts to

a d

epth

of 0

.60

m.

da C

osta

and

Cru

scio

l (2

016)

Mai

ze60

/26/

00-

2.0

1.77

-4.9

911

1-18

2Li

min

g in

crea

sed

soil

pH fr

om 4

.92-

5.46

and

redu

ced

EA fr

om 0

.25-

0.10

cm

ol k

g-1.

Opa

la e

t al.

(201

8)

Faba

bea

n18

/20/

00.

0-5.

00.

81-1

.47

45-5

3Li

min

g in

crea

sed

soil

pH fr

om 5

.10-

5.91

and

redu

ced

EA fr

om 1

.31-

0.12

cm

ol k

g-1.

Age

gneh

u et

al.

(200

6)

Muc

una

flage

llipe

s-

0.0-

4.0

1.39

-2.8

245

-103

Lim

ing

incr

ease

d so

il pH

from

4.3

2-6.

11.

Agb

a et

al.

(201

7)

Pota

to0/

0/0/

-10

/40/

100

0.0-

3.5

10.0

3-30

.67

59-3

32Li

min

g in

crea

sed

soil

pH fr

om 4

.8-5

.47.

Hai

le a

nd B

oke

(200

9)

NPK

(kg

ha-1

)FY

M (t

ha

-1)

Yie

ld (t

ha

-1)

% in

crea

se o

ver

cont

rol

Faba

bea

n18

/0-5

2/0

0.0-

8.0

0.99

-2.2

142

-123

Add

ition

of F

YM

incr

ease

d so

il pH

from

4.5

1-5.

22, N

, P, a

nd

exch

ange

able

cat

ions

.A

gegn

ehu

and

Bek

ele

(200

5b)

Pota

to0/

0/0/

-10

/40/

100

0-20

17-5

413

4-21

7H

aile

and

Bok

e (2

011)

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SOIL ACIDITY MANAGEMENT 38

Table 12. Estimated returns to lime use in wheat cultivation based on experimental results of 2015

Item Without lime With lime

Lime application (t ha-1) 0 2.2

Grain yield (t ha-1) 0.9 1.98

Adjusted grain yield (t ha-1)1 0.9 1.584

Cost of lime at farm gate (birr) 0 4,400

Labor cost for lime application at birr 50/day) 0 800

Total Cost of lime use (birr ha-1) 0 5,200

Grain price (birr t-1) 11,000 11,000

Gross value of output (birr ha-1) 9,900 17,424

Net returns to lime use (birr ha-1) 0 7,524

Net added value due to lime use (birr ha-1) 2,324

Note: 1The experimental wheat grain yield from lime application is adjusted downwards by 20% to estimate what a typical farmer would be more likely to obtain under farmer conditions. 1USD = Birr 27.27

At a national level, widespread use of lime is expected to have remarkable economic benefits. Accurate quantitative estimates of national benefits from the use of agricultural lime, however, are fraught with uncertainties associated with the rate of increase in agricultural lime production, transportation and distribution. Such estimates are also sensitive to the level of public-private partnership attained in the provision of critical services such as credit and advisory services to farmers. Nonetheless, despite such uncertainties, three factors are crucial to estimating the possible impact of increased agricultural lime production and distribution in Ethiopia. The first factor relates to estimating the value added to the national economy from the increased production resulting from the use of agricultural lime. The second factor relates to savings in foreign exchange (lower import bills) due to decreased imports of basic agricultural commodities. The third factor is associated with the value of possible increases in exports of agricultural products such as soybean and coffee. Owing to lack of micro data and information, value added estimates to the national economy are based on productivity improvements (Table 10). Accordingly, assuming wheat is planted to all land rehabilitated and the same average returns prevail under actual production conditions as shown in Table 13, the total gross returns from the use of lime would be about birr 38.3 million in 2015 (base scenario). Further, assuming reclamation of acid soils goes as planned by the MoANR, the same average returns prevail under actual production conditions and current input-output prices hold in the future, the annual total gross and net value added to the economy from the use of lime would be birr 1.7 billion and 0.53 billion, respectively, by the end of GTP II. Correspondingly, the amount of lime required to gain the indicated value added would be about 500,000 tons. It is worth noting that only a small fraction of the acid soil areas are planned to be rehabilitated by the end of GTP II.

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Table 13. Estimated value added to the Ethiopian economy from lime use under the assumption of a single crop, wheat

ItemYear

2015 2020

Area to be rehabilitated (000’ ha)1 5.1 226

Lime required (000’ ton) 11.22 497.2

Value added to gross national income (‘000 birr) 38,372 1,700,424

Net value added to crop production ‘000 birr)2 11,852 525,224

1Reclamation of acid soil goes as planned by MoANR and reaches 256,000 ha by end of GTP II period.2Values for the year 2015 represents the base scenario while 2020 value refer to end of GTP II.

The other important impact of widespread use of lime in Ethiopia would be a substantial saving in foreign exchange due to lower import bills from reduced or complete substitution of imports of basic commodities such as wheat. In 2012, the country imported 1.1 million tons of wheat at a cost of 332.97 million USD (FAO, 2014). Such imports, however, could be eliminated by raising wheat productivity from the current average of 2.45 t ha-1 (CSA, 2016) to 3.13 t ha-1.

Value chain and transaction costs of lime crushing

Understanding the production of lime is based on a site visit and interview with the manager of the only public lime crushing plant in Amhara region. The facility is situated on a 2.5 ha of land, approximately 2 km from the Addis-Bahirdar highway near the town of Dejen. The plant employs 50 casual workers, with a wage rate of birr 35 per day; and a supervisor and a manager both paid by the Bureau of Agriculture. The annual salaries for the supervisor and manager are assumed at birr 36,000 and birr 60,000, respectively.

The manager has been found to be very knowledgeable about the lime crushing operation, but has very little role in the operational planning, marketing, and distribution of lime. The prices of both inputs and outputs of the plants are administratively determined. For instance, all workers are paid a uniform wage rate, which is half the going rate of day laborers in the area and is not based on individual work assignment or productivity. Similarly, the price of packaged lime has been fixed at birr 75 at the factory gate. These actions have important implications for efficiency of the value chain, which have been discussed under three broad segments in the lime value chain: input procurement (upstream), processing (mid-stream), and the distribution to farmers (downstream). The value chain segments, activities and costs are denoted in Figure 6.

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Figure 6. Value chain segments, activities, and costs.

Source: Warner et al. (2016)

Upstream or input procurement

The procurement of inputs for lime crushing, carried out during the rainy season, involves collection of limestone from a nearby location. This laborious process requires digging out large lime rocks, breaking them into smaller pieces, and loading and unloading them to a truck— all done manually. The Bureau of Agriculture and Rural Development (BoARD) provides a truck with a driver for 1 to 1.5 months depending on the projected demand. While the truck has higher capacity, due to difficult terrain and road conditions, it ships only about 5 tons per trip and makes 5-6 trips a day. The casual employees work about six months in input procurement. Assuming a rental cost of birr 4000/day for a truck, costs for 45 days will be birr 180,000, manual labor costs for six months would be birr 315,000 and supervisory labor costs are estimated at birr 48,000. Since the casual workers are also responsible for loading and unloading, there are no additional costs involved in the transportation. Hence, with simplifying assumptions, the total cost of procurement would be birr 543,000.

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Mid-stream or processing

The processing or lime crushing is carried out during the dry season typically from January to June, with operation peaking during March to May. Currently, the plant has a capacity of 10 tons per day, if the operation is uninterrupted. A second crusher, with a daily capacity of 30 tons a day, is under construction at the same location. While machinery has been imported and a building has been constructed, it was not clear as to when the new crusher might be operational. In the 2014/15 season, the plant produced a total of 1500 tons, which is equivalent to 150 days of operation at full capacity. Deriving a rough cost estimate for this segment requires data on the costs of labor, electricity, depreciation, and the opportunity costs of capital. We obtained data on labor and electricity costs only. The manual wage bill is roughly birr 315,000 (180×50×35), and administration was assumed to be birr 48,000. The electricity bill of birr 1000 was assumed to be a monthly cost and electricity use was determined by summing monthly costs and dividing by 180 days of crusher operation, outside this period it was assumed that electricity use would be negligible. For the crusher it was projected a one-time fixed cost of birr 1.1 million1 ($50,000 USD), operated for five years at approximately 180 days per year. Annual spare parts/maintenance costs, etc. were estimated to be 10% of crusher purchase cost. Bag costs are birr 10 for each bag. Finally, discussions with experts estimated a constructed water-resistant storage facility to be birr 467 m-3. Applying this towards a facility that is 15m×30m×5m (enough to store 2250 tons) and applying to 10 years of operation arrives at a daily rate of birr 288. Opportunity costs were not included. The total daily rate for processing equals birr 5478 and total costs come to birr 986,000 for annual operation of 180 days.

Downstream/distribution

The manager of the plant has no role in the distribution and marketing of lime. The volume of production and the marketing depend on an estimated demand of lime, which is generated through a multi-stage planning process, starting at a Kebele level. The initial assessment is carried out by the extension agents at the Kebele level, which are then aggregated up to a district level. The region reexamines district estimates and comes up with the final official estimates. Public tenders are then issued to procure the estimated quantity of lime, by districts, at a predetermined price (uniform/pan territorial prices). The cooperative unions typically win these tenders. From the cooperative unions, lime is transported to the primary cooperatives for farmers to collect. Table 14 presents some rough estimates from the field interview.

1 This estimate was obtained from a business website question and answer forum (www.quora.com/What-is-the-price-of-a-small-jaw-crusher-for-a-limestone-crushing-plant), accessed on May 24, 2016.

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Table 14. Cost of structure of agricultural lime along with the value chain

Particular Price (birr/100 kg)

Price at crushing plant 75

Transport to union 100

Transport to primary cooperative 30

Primary coop to farmers field 5

Landed costs at farm gate 210

Costs of application (the cost of oxen could be subsumed with planting but is assumed to be inde-pendent cost here)

Labor 16 man days; rental costs of a pair of bullocks (2*16*50= 1600

Per hectare costs:

Moderately acidic—2 t ha-1 application 5,800

Highly acidic—4 t ha-1 application 10,000

Planning process

Lime production, marketing, and distribution depend on an elaborate planning process, involving public officials at various administrative levels. There are six distinct steps in the planning process, as depicted below in Figure 7.

Figure 7. Zonal level planning processSource: Warner et al. (2016)

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There are two basic problems with the process: First, the soil testing is too time-consuming. Improving soil evaluation and remedies needs to be greatly streamlined. This will be further elaborated, but for now, it is fair to conclude that not all these steps are necessary. In highly acidic areas, policy campaign can be launched based on the existing information and on the assumption of an aggregate demand. The challenge here is determining appropriate policy option(s). Policy options are either providing lime through government channels; or exploring private-public partnerships. Both options need further assessment. However, given the current speed of implementation, government–led interventions are likely to take a very long time to amend Ethiopia’s acidic soils. For instance, we have learned that Awi zone alone has 177,000 ha of acidic soils. The dose of lime depends on the pH level, but ranges from about one t ha-1 in moderately acidic soils to 3.8 t ha-1 in highly acidic soils. In 2014/15, average application rate was about 2.0 t ha-1. This implies that the total demand for Awi would be 344,000 tons. Given Dejen can produce only 1500 tons a year, even if the entire production from Dejen plant is allocated to Awi, it would take over 200 years to amend the acid soil in this zone. The other point is that demand assessment and lime distribution are not based on up-to-date information. In fact, actions of the current year depend on the previous year. This is clear once timing of activities is mapped. For instance, the demand for lime for main-season of a given year is announced in September of the previous year. This is because the test results are available in February of the previous year. After demand is announced, it takes 4-5 months for lime to be distributed to the Cooperative Unions; and another 2-3 months to supply to the farmers through primary cooperatives.

Promotion of ISFM Approaches

Despite the production of substantial quantities of crop residues and manures in the country, they are not returned to soil for amelioration soil fertility due to competing uses. Farmers generally use crop residues as livestock feed because of their higher value as feed than as soil improver. Manure is used as an energy source instead of using it as soil amendment due to lack of alternative energy sources. With the use of compost and biochar, the organic resource can be recycled back to the farm. Composting of both crop residues and manure together or carbonization of part of them to biochar can reduce the volume of organic resources, which means less labor/cost to transport them back to the field. Biochar application to soils may enable farmers to get the benefit of resistant organic matter and nutrients, if they have not been leached out or denitrified during the composting process, but the labile carbon may be lost to the atmosphere. The labile carbon would benefit the soil because it can feed soil organisms, which are responsible for several beneficial processes in the soil (Agegnehu et al., 2017). In terms of liming acid soils, studies indicated that biochar is able to raise soil pH at about one-third the rate of lime, increases Ca levels and reduce Al toxicity on acid soils (Glaser et al., 2002; Lehmann et al., 2003; Steiner, 2007).

Appropriate policies towards sustainable land use intensification and the necessary institutions and mechanisms to implement and evaluate these are also important to facilitate the adoption of ISFM. Specific policies to address the restoration of degraded soils may also be required as investments to achieve, as this may be too high to be met by farmers alone. Although the utilization of improved seeds and fertilizers has significantly increased crop productivity, application of ISFM could considerably increase low agronomic efficiency (Vanlauwe et al., 2010; Vanlauwe and Zingore, 2011), with all the consequent economic benefits to farmers. While efforts to promote the seed and fertilizer technology has been under way, activities such as development of site-specific decision guides that enable tackling more complex issues can be initiated to

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guide farming communities towards complete ISFM, including suitable organic matter management and adaptation of technologies to be achieved at the local level. Overall, in the face of climate change, adoption of ISFM has the potential not only to improve farm productivity and farmers’ income, but also to result in

environmental benefits in tropical agro-ecosystems.

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9CONCLUSION

Sustainable soil management practices and the maintenance of soil quality are central issues to agricultural sustainability. Soil acidity and associated low nutrient availability are among the major constraints to crop production. Soil reaction is one of the physiological characteristics of the soil solution expressed in terms of pH which indicates whether the soil is acid, alkaline, or neutral. It exercises significant on many soil properties including nutrient availability, biological activity, and soil physical condition. The practice of liming acid soils to mitigate soil acidity and reduce phytotoxic levels of Al and Mn has been recognized as necessary for optimal crop production in acid soils. However, application of lime should be considered as an approach to improve soil pH to optimize nutrient availability for optimum plant growth and yield, otherwise, it is not an end goal by itself to achieve potential yield. Liming should be coupled with the applications of optimum rates of inorganic and organic fertilizers, particularly P and K fertilizers. Moreover, there is a need for identifying areas where lime application brings significant change and benefit in crop yield. Overall, liming should be considered as a soil amendment to raise soil pH to the level that is suitable for maximum nutrient availability, plant growth, and crop yield.

The rate of soil acidification can also be reduced through integrated soil and crop management. Integrated soil fertility management approach can enhance both soil productivity and crop yield. It is evident that application of organic residues enhances buildup of nutrients in the soil and after successive years of application, the dose of nutrients to be applied as inorganic or organic forms will gradually decrease. Residual effects of organic sources on crop production and soil properties may last for several years and hence, their profitability could not be precisely estimated in the short-term, and rather their effect is clearly seen in the long term. Application of organic residues not only increases the nutrient content of soils but also improves their physical and biological properties. Matching applied nitrogen and sulfur with crop needs may also reduce input costs while reducing acidification. Other practices involve choosing less acidifying fertilizers or improving time of application although such practices may increase input and management costs. When considering changes, these costs need to be weighed against an eventual reduction in the cost of lime application.

Crops differ widely in their ability to tolerate acid soil conditions. Coffee, tea, tuber, pineapple, certain pasture grasses, and legumes are tolerant of high levels of Al saturation, while legumes, sorghum, and cotton are intolerant. Important varietal differences in relation to Al tolerance exist in rice, corn, wheat, beans, and soybeans. These differences provide a good possibility for selection and breeding plants for improved tolerance to soil acidity, a low cost and effective alternative to the high cost of amending acid soil using lime. In general, the integrated use of all the available resources including acid tolerant crops and crop species, which improve and sustain soil and agricultural productivity, is of great practical significance. Overall, acid soil management needs to emphasize strategic research, integrating soil and water management with improved crop varieties to generate prototype and environmentally benign technologies for sustained food production within a framework of appropriate socio-economic and policy considerations.

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REFERENCESAbebe, M. (1998). “Nature and management of Ethiopian soils,” Alamaya University of Agriculture,

Alemaya, Ethiopia.

Abebe, M. (2007). “Nature and management of acid soils in Ethiopia,” Haramaya University, Haramaya,

Ethiopia.

Abewa, A., Yitaferu, B., Selassie, Y. G., and Amare, T. T. (2014). The role of biochar on acid soil reclamation

and yield of Teff (Eragrostis tef [Zucc] Trotter) in Northwestern Ethiopia. J. Agric. Sci. 6, 1-12.

Adams, F. (1990). “Soil acidity and liming,” Second edition/Ed. Am. Soc. Agron., Wisconsin, USA.

Adhikari, B., and Karki, K. B. (2006). Effect of potassium on potato tuber production in acid soils of

Malepatan, Pokhara. Nepal Agric. Res. J. 7, 42-48.

Agba, O., Asiegbu, J., Ikenganyia, E., Anikwe, M., Omeje, T., and Adinde, J. (2017). Effects of Lime on

Growth and Yield of Mucuna flagellipes (Vogel ex Hook) in an Acid Tropical Ultisol. J. Agric. Ecol.

Res. Int. 12, 1-14.

Agegnehu, G., and Amede, T. (2017). Integrated soil fertility and plant nutrient management in tropical

agro-ecosystems: A review. Pedosphere 27, 662-680.

Agegnehu, G., and Bekele, T. (2005a). On-farm Integrated soil fertility managment in wheat on nitisols of

centreal Ethiopian highlands. Ethiop. J. Nat. Resources 7, 141-155.

Agegnehu, G., and Bekele, T. (2005b). Phosphorus ferilizer and farmyard manure effects on the growth

and yield of Faba Bean and some soil chemical properties in acidic nitisols of the central highlands of

Ethiopia. Ethiop. J. Nat. Resources. 7, 23-39.

Agegnehu, G., Fikre, A., and Tadesse, A. (2006). Cropping Systems, Soil Fertility and Crop Management

Research on Food Legumes in the Central Highlands of Ethiopia. In “A Review of Major Achievements

of a Decade” (K. Ali, G. Keneni, S. Ahmed, R. S. Malhotra, S. Beniwal and K. Makkouk, eds.), pp. 135-

145. ICARDA, Addis Ababa, Ethiopia.

Agegnehu, G., and Sommer, K. (2000a). Optimization of the efficiency of phosphate fertilizers in acidic-

ferralitic soils of the humid tropics. Ethiopian Journal of Natural Resources 2, 63-77.

Agegnehu, G., and Sommer, K. (2000b). Optimization of the efficiency of phosphate fertilizers in acidic-

ferralitic soils of the humid tropics. Ethiop. J. Nat. Resources 2, 63-77.

Agegnehu, G., Srivastava, A., and Bird, M. I. (2017). The role of biochar and biochar-compost in improving

soil quality and crop performance: a review. Appl. Soil Ecol. 119, 156-170.

Agoumé, V., and Birang, A. (2009). Impact of land-use systems on some physical and chemical soil

properties of an oxisol in the humid forest zone of southern Cameroon. Tropicultura 27, 15-20.

Page 54: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 47

Akhtar Schuster, M., Thomas, R. J., Stringer, L. C., Chasek, P., and Seely, M. (2011). Improving the enabling

environment to combat land degradation: Institutional, financial, legal and science‐policy challenges

and solutions. Land Degradation and Development 22, 299-312.

Amede, T., Belachew, T., and Geta, E. (2001). Reversing the degradation of arable land in the Ethiopian

highlands. In “Managing Africa’s Soils”, pp. 1-29, Addis Ababa, Ethiopia.

Anetor, M. O., and Akinrinde, E. A. (2007). Lime effectiveness of some fertilizers in a tropical acid Alfisol.

J. Central Eur. Agric. 8, 17-24.

Antoniazzi, L., Nassar, A., Moura, P., and Kimura, W. (2013). Technologies in Brazilian agriculture and

potential for cooperation with Africa pp. 64. Institute for International Trade Negotiations, Brazil.

Asrat, M., Gebrekidan, H., Yli-Halla, M., Bedadi, B., and Negassa, W. (2014). Effet of integrated use of

lime manure and mineral P fertilizer on bread wheat (Triticum aestivum) yield, uptake and status of

residual soil P on acidic soils of Gozamin district, northwestern Ethiopia. Agric. Forest. Fish. 3, 76-85.

ATA (2014). Soil Fertility Mapping and Fertilizer blending. Agricultural Transformation Agency (ATA),

Addis Ababa, Ethiopia.

Ayalew, A. (2007). The influence of applying lime and NPK fertilizers on yield of maize and soil properties

on acid soil of Areka, Southern Region of Ethiopia. Innov. Syst. Design Engin. 2, 33-42.

Bai, Z. G., Dent, D. L., Olsson, L., and Schaepman, M. E. (2008). Proxy global assessment of land degradation.

Soil Use Manage. 24, 223–234.

Baquy, M., Li, J. Y., Xu, C. Y., Mehmood, K., and Xu, R. K. (2017). Determination of critical pH and Al

concentration of acidic Ultisols for wheat and canola crops. Solid Earth 8, 149-159.

Barber, S. A. (1984). Liming materials and practices. In ‘‘Soil Acidity and Liming’’ (F. Adams, Ed.), 2nd Ed.

pp. 171–209. ASA-CSSA-SSSA, Madison, Wisconsin.

Barcelo, J., and Poschenrieder, C. (2002). Fast root growth responses, root exudates, and internal

detoxification as clues to the mechanisms of aluminium toxicity and resistance: a review. Environ.

Exp. Botany 48, 75-92.

Barrow, N. J. (1984). Modeling the effects of pH on phosphate sorption by soils. J. Soil Sci. 35, 283-297.

Behera, S. K., and Shukla, A. K. (2015). Spatial distribution of surface soil acidity, electrical conductivity,

soil organic carbon content and exchangeable potassium, calcium and magnesium in some cropped

acid soils of India. Land Degrad. Dev. 26, 71-79.

Bekele, T., and Höfner, W. (1993). Effects of different phosphate fertilizers on yield of barley and rapeseed

on reddish brown soils of the Ethiopian highlands. Fertilizer Res. 34, 243-250.

Page 55: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 48

Bekere, W., Kebede, T., and Dawud, J. (2013). Growth and Nodulation Response of Soybean (Glycin max

L.) to Lime, Bradyrhizobium japonicum and Nitrogen Fertilizer in Acid Soil at Melko, South Western

Ethiopia. Intenational Journal of Soil Science 8, 25-31.

Beyene, D. (1987). Effects of liming and N and P Fertilizers on grain yield of barley. Ethiop. J. Agric. Sci.

9, 1-13.

Bore, G., and Bedadi, B. (2015). Impacts of land use types on selected soil physico-chemical properties of

Loma Woreda, Dawuro zone, southern Ethiopia. Sci. Technol. Arts Res. J. 4, 40-48.

Bore, G., and Bedadi, B. (2016). Response Wheat (Triticum aestivum L.) to Liming of Acid Soils

under Different Land Use Systems of Loma Woreda, Dawuro Zone, Southern Ethiopia. Journal of

Environment and Earth Science 6, 99-108.

Brady, N., and Weil, R. (2016). “The nature and properties of soils,” Pearson Education, Columbus, EUA.

Bronick, C. J., and Lal, R. (2005). Soil structure and management: a review. Geoderma 124, 3-22.

Brown, T. T., Koeing, R. T., Huggins, D. R., Harsh, J. B., and Rossi, R. E. (2008). Lime effects on soil acidity,

crop yield, and Al chemistry in direct-seeded cropping systems. Soil Sci. Soc. Am. J. 72, 634-640.

Buni, A. (2014). Effects of Liming Acidic Soils on Improving Soil Properties and Yield of Haricot Bean. J.

Environ. Anal. Toxicol. 5, 1-4.

Chimdi, A., Gebrekidan, H., Kibret, K., and Tadesse, A. (2012). Status of selected physicochemical

properties of soils under different land use systems of western Oromia, Ethiopia. J. Biodiv. Environ.

Sci. 2, 57-71.

Chimdi, A., Gebrekidan, H., Kibret, K., and Tadesse, A. (2013). Changes in soil chemical properties as

influenced by liming and its effects on barely grain yield on soils of different land use system of East

Wollega, Ethiopia. World Applied Sciences Journal 24, 1435-1441.

Conant, R. T., Smith, G. R., and Paustian, K. (2003). Spatial variability of soil carbon in forested and

cultivated sites. J. Environ. Quality 32, 278-286.

Cornelissen, G., Nurida, N. L., Hale, S. E., Martinsen, V., Silvani, L., and Mulder, J. (2018). Fading positive

effect of biochar on crop yield and soil acidity during five growth seasons in an Indonesian Ultisol.

Sci. Total Environ. 634, 561-568.

Coventry, D. R. (1991). The injection of slurries of lime, associated with deep tillage, to increase wheat

production on soils with subsoil acidity. In “Plant–soil interactions at low pH” (R. J. e. a. Wright, ed.),

pp. 437-445. Kluwer Academic Publ., Dordrecht, the Netherlands.

CSA (2016). Report on Area and Production of Major Crops. Agricultural Sample Survey 2013/14, CSA

(Central Statistical Agency). Volume 1. Addis Ababa, Ethiopia

da Costa, C. H. M., and Crusciol, C. A. C. (2016). Long-term effects of lime and phosphogypsum application

on tropical no-till soybean–oat–sorghum rotation and soil chemical properties. European Journal of

Agronomy 74, 119-132.

Page 56: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 49

de Sant-Anna, S. A., Jantalia, C. P., Sá, J. M., Vilela, L., Marchão, R. L., Alves, B. J., Urquiaga, S., and Boddey,

R. M. (2017). Changes in soil organic carbon during 22 years of pastures, cropping or integrated crop/

livestock systems in the Brazilian Cerrado. Nutr. Cycl. Agroecosyst. 108, 101-120.

Desalegn, T., Alemu, G., Adella, A., and Debele, T. (2017). Effect of lime and phosphorus fertilizer on Acid

soils and barley (Hordeum vulgare L.) performance in the central highlands of Ethiopia. Exp. Agric.

53, 432-444.

Duffera, M., and Robarge, W. P. (1999). Soil characteristics and management effects on phosphorus

sorption by highland plateau soils of Ethiopia. Soil Sci. Soci. Am. J. 63, 1455-1462.

Duncan, M. R. (2002). Soil acidity and P deficiency: Management strategies for the northern Tablelands of

NSW. NSW Agriculture, Armidale, Australia.

EAAPP (Eastern Africa Agricultural Productivity Project) (2015). “Terminal report for research component.

Ethiopian Institute of Agricultural Research (EIAR), EAAPP research coordination office.” Ethiopian

Institute of Agricultural Research, Addis Ababa, Ethiopia.

Edmeades, D., Ridley, A., and Rengel, Z. (2003). Handbook of soil acidity. Handbook of soil acidity.

Eghball, B., Ginting, D., and Gilley, J. E. (2004). Residual effects of manure and compost applications on

corn production and soil properties. Agron. J. 96, 442-447.

Eswaran, H., Almaraz, R., van den Berg, E., and Reich, P. (1997a). An assessment of the soil resources of

Africa in relation to productivity. Geoderma 77, 1-18.

Eswaran, H., Reich, P., and Beinroth, F. (1997b). Global distribution of soils with acidity. Plant-Soil

interactions at low pH, 159-164.

Fageria, N., and Baligar, V. (1997). Integrated plant nutrient management for sustainable crop production-

an overview. Int. J. Trop. Agric. 15, 1-18.

Fageria, N., and Baligar, V. (2008). Ameliorating soil acidity of tropical Oxisols by liming for sustainable

crop production. Adv. Agron. 99, 345-399.

Fageria, N., Baligar, V., and Zobel, R. (2007). Yield, Nutrient Uptake, and Soil Chemical Properties as

Influenced by Liming and Boron Application in Common Bean in a No‐Tillage System. Comm. Soil

Sci. Plant Anal. 38, 1637-1653.

Fageria, N. K. (2009). “The use of nutrients in crop plants,” CRC Press: Taylor and Francis Group, USA.

Fageria, N. K., and Nascente, A. S. (2014). Management of soil acidity of South American soils for

sustainable crop production. Adv. Agron. 128, 221-275.

FAO (2014). Analysis of price incentives for wheat in Ethiopia. FAO, Rome, Italy.

Farina, M. P. W. (1997). 1997. Management of subsoil acidity in environments outside the humid tropics.

p. 179–190. In A.C. Moniz et al. (ed.) Plant–soil interactions at low pH: Sustainable agriculture and

forestry production. Brazilian Soil Sci. Soc., Campinas, Brazil.

Page 57: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 50

Farina, M. P. W., and Channon, P. (1988). Acid-subsoil amelioration: nure, Tokyo. I. A comparison of

several mechanical procedures. Soil Sci. Soc. Am. J. 52, 169–175.

Farina, M. P. W., Channon, P., and Thibaud, G. R. (2000). A Comparison of strategies for ameliorating

subsoil acidity: II. Long-term soil effects. Soil Sci. Soc. Am. J. 64, 652–658.

Fox, R. (1979). Soil pH, aluminum saturation, and corn grain yield. Soil Sci. 127, 330-334.

Garvin, D. F., and Carver, B. F. (2003). Role of the genotype in tolerance to acidity and aluminum toxicity.

Handbook of soil acidity. Marcel Dekker, New York, 387-406.

Gebrekidan, H., and Negassa, W. (2006). Inmpact of land use and management practices on chemical

properties of some soils of Bako area, Western Ethiopia. Ethiop. J. Nat. Resources. 8, 177-197.

Glaser, B., Lehmann, J., and Zech, W. (2002). Ameliorating physical and chemical properties of highly

weathered soils in the tropics with charcoal–a review. Biol. Fert. Soils 35, 219-230.

Guanziroli, C. E., and Basco, C. A. (2014). Construction of agrarian policies in Brazil: the case of the

National Program to Strengthen Family Farming (PRONAF). Comuniica, 44-63.

Guo, J. H., Liu, X. J., Zhang, Y., Shen, J. L., Han, W. X., Zhang, W. F., Christie, P., Goulding, K. W. T.,

Vitousek, P. M., and Zhang, F. S. (2010). Significant Acidification in Major Chinese Croplands. Science

327, 1008-1010.

Haile, H., Asefa, S., Regassa, A., Demssie, W., Kassie, K., and Gebrie, S. (2017). Extension manual for acid

soil management (unpublished report). (A. T. A. (ATA), ed.), Addis Ababa, Ethiopia.

Haile, W., and Boke, S. (2009). Mitigation of soil acidity and fertility decline: Challenges for sustainable

livelihood improvement: Evidence from southern region of Ethiopia. In “Sustainable land management

and poverty alleviation “, pp. 131-143. Ethiopian Development Research Institute, Addis Ababa.

Haile, W., and Boke, S. (2011). Response of Irish potato (Solanum tuberosum) to the application of

potassium at acidic soils of Chencha, Southern Ethiopia. Int. J. Agric. Biol. 13, 595-598.

Haynes, R., and Mokolobate, M. (2001). Amelioration of Al toxicity and P deficiency in acid soils by

additions of organic residues: a critical review of the phenomenon and the mechanisms involved.

Nutr. Cycl. Agroecosyst. 59, 47-63.

Haynes, R., and Naidu, R. (1998). Influence of lime, fertilizer and manure applications on soil organic

matter content and soil physical conditions: a review. Nutr. Cycl. Agroecosyst. 51, 123-137.

Helyar, K. R. (1991). The management of acid soils. p. 365–382. In R.J. Wright et al. (ed.) Plant–soil

interactions at low pH. Kluwer Academic Publ., Dordrecht, the Netherlands.

Hillard, J., Haby, V., and Hons, F. (1992). Annual ryegrass response to limestone and phosphorus on an

Ultisol. J. Plant Nutr. 15, 1253-1268.

Horsnell, L. J. (1985). The growth of improved pastures on acid soils: III. Response of lucerne to phosphate

as affected by calcium and potassium sulphates and soil aluminum levels. Aust. J. Exp. Agric. 25,

557–561.

Page 58: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 51

Hue, N. (1992). Correcting soil acidity of a highly weathered Ultisol with chicken manure and sewage

sludge. Comm. Soil Sci. Plant Anal. 23, 241-264.

Junquan, Z., Michalk, D., Yifei, W., Kemp, D., Guozhen, D., and Nicol, H. (2007). Effect of phosphorus,

potassium and lime application on pasture in acid soil in Yunnan Province, China. New Zealand J.

Agric. Res. 50, 523-535.

Kamprath, E. J. (1984). Crop response to lime on soils in the tropics. Soil acidity and liming, 349-368.

Kamprath, E. J., and Adams, F. (2010). Soil acidity and liming. In “Century of soil science”, pp. 103-107. Soil

Science Society of North Carolina, North Carolina, USA.

Kang, B., and Juo, A. (1986). Effect of forest clearing on soil chemical properties and crop performance.

Land clearing and development in the tropics, 383-394.

Khandakhar, S. M. T., Rahman, M. M., Uddin, M. J., Khan, S. A. U., and K.G., Q. (2004). 2004. Effect of

lime and potassium on potato yield in acid soil. Pak. J. Biol. Sci. 7, 380- 383.

Kidanemariam, A., Gebrekidan, H., Mamo, T., and Fantaye, K. T. (2013). Wheat crop response to liming

materials and N and P fertilizers in acidic soils of Tsegede highlands, northern Ethiopia. Agric. Forest.

Fish. 2, 126-135.

Klink, C. A. (2014). Policy Intervention in the Cerrado Savannas of Brazil: Changes in the Land Use and

Effects on Conservation. A. Consorte-McCrea, & E. Ferraz Santos, Ecology and Conservation of the

Maned Wolf: Multidisciplinary Perspectives, 293-308.

Kochian, L. V., Hoekenga, O. A., and Pineros, M. A. (2004). How do crop plants tolerate acid soils?

Mechanisms of aluminum tolerance and phosphorous efficiency. Annu. Rev. Plant Biol. 55, 459-493.

Krug, E. C., and Frink, C. R. (1983). Acid rain on acid soil: a new perspective. Science 221, 520-525.

Lal, R. (2009). Soils and food sufficiency: A review. In “Sustainable agriculture”, pp. 25-49. Springer.

Lal, R. (2015). Restoring soil quality to mitigate soil degradation. Sustainability 7, 5875-5895.

Lawlor, D. (2004). Mengel, K. and Kirkby, EA Principles of plant nutrition. Oxford University Press.

Lehmann, J., da Silva, J. P., Steiner, C., Nehls, T., Zech, W., and Glaser, B. (2003). Nutrient availability

and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer,

manure and charcoal amendments. Plant Soil 249, 343-357.

Lemenih, M., Karltun, E., and Olsson, M. (2005). Assessing soil chemical and physical property responses

to deforestation and subsequent cultivation in smallholders farming system in Ethiopia. Agric.

Ecosyst. Environ. 105, 373-386.

Li, S., Duan, Y., Guo, T., Zhang, P., He, P., Johnston, A., and Shcherbakov, A. (2015). Potassium management

in potato production in Northwest region of China. Field Crops Research 174, 48-54.

Ma, J. F., Ryan, P. R., and Delhaize, E. (2001). Aluminium tolerance in plants and the complexing role of

organic acids. Trends Plant Sci. 6, 273-278.

Page 59: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 52

Mahler, R., Saxena, M., and Aeschlimann, J. (1988). Soil fertility requirements of pea, lentil, chickpea and

faba bean. In “World crops: Cool season food legumes”, pp. 279-289. Springer.

Mamo, T., and Haque, I. (1991). Phosphorus status of some Ethiopian soils, II. Forms and distribution of

inorganic phosphates and their relation to available phosphorus. Trop Agric 68, 2-8.

Marschner, H. (2011). “Marschner’s mineral nutrition of higher plants,” Academic press, London.

McKenzie, R., Penney, D., Hodgins, L., Aulakb, B., and Ukrainetz, H. (1988). The effects of liming on an

ultisol in Northern Zambia. Comm. Soil Sci. Plant Anal. 19, 1355-1369.

Michael, C. (2000). Soil acidity and liming. Part 4. Auburn University, Alabama Cooperative Extension

Sustem. USA.

Opala, P. A., Odendo, M., and Muyekho, F. N. (2018). Effects of lime and fertilizer on soil properties and

maize yields in acid soils of Western Kenya. African Journal of Agricultural Research 13, 657-663.

Parfitt, R. L. (1978). Anion adsorption by soils and soil minerals. Adv. Agron. 20, 323-359.

Paul, E. A. (2014). “Soil microbiology, ecology and biochemistry,” Third/Ed. Academic press, Elsevier Inc.,

London, UK.

Pilbeam, D. J., and Morley, P. S. (2007). Calcium. Hand book of plant nutrition. In: Barker, A.V., Pilbeam,

D.J. (eds.). CRC: Taylor and Francis, New York, pp. 121-144.

Poschenrieder, C., Gunsé, B., Corrales, I., and Barceló, J. (2008). A glance into aluminum toxicity and

resistance in plants. Sci. Total Environ. 400, 356-368.

Poss, R., and Saragoni, H. (1992). Leaching of nitrate, calcium and magnesium under maize cultivation on

an oxisol in Togo. Fertilizer research 33, 123-133.

Prasad, R., and Power, J. F. (1997). “Soil fertility management for sustainable agriculture,” CRC press.

Regassa, H., and Agegnehu, G. (2011). Potentials and limitations of acid soils in the highlands of Ethiopia:

a review. In “Barley research and development in Ethiopia” (B. Mulatu and S. Grando, eds.), pp. 103-

112. ICARDA, Aleppo, Syria.

Rengel, Z. (2011). Soil pH, soil health and climate change. In “Soil health and climate change”, pp. 69-85.

Springer.

Ritchey, E. L., Murdock, L. W., Ditsch, D. C., McGrath, J. M., and Sikora, F. J. (2016). Agricultural lime

recommendations based on lime quality. In “Agricultural and Natural Resources Publication” (U. o.

Kentucky, ed.), pp. 1-7, LexIngton, KY,.

Ritchey, K. D., Feldhake, C. M., Clark, R. B., and Sousa, D. M. G. (1995). Improved water and nutrient

uptake from subsurface layers of gypsum-amended soils. p. 157–181. In Agricultural utilization of

urban and industrial by-products. ASA Spec. Publ. 58. ASA, Madison, WI.

Roem, W. J., and Berendse, F. (2000). Soil acidity and nutrient supply ratio as possible factors determining

changes in plant species diversity in grassland and heathland communities. Biol. Conserv. 92, 151-

161.

Page 60: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 53

Saıdou, A., Janssen, B., and Temminghoff, E. (2003). Effects of soil properties, mulch and NPK fertilizer

on maize yields and nutrient budgets on ferralitic soils in southern Benin. Agric. Ecosyst. Environ.

100, 265-273.

Sample, E., Soper, R., and Racz, G. (1980). Reactions of phosphate fertilizers in soils. The role of phosphorus

in agriculture, 263-310.

Sanchez, P. A. (1977). Properties and Management of Soils in the Tropics. Soil Sci. 124, 1-187.

Sanchez, P. A., and Uehara, G. (1980). Management considerations for acid soils with high phosphorus

fixation capacity. The role of phosphorus in agriculture, 471-514.

Sertsu, S., and Ali, A. (1983). Phosphorus sorption characteristics of some Ethiopian soils. Ethiop. J. Agric.

Sci. 5, 1-12.

Shainberg, I., Sumner, M. E., Miller, W. P., Farina, M. P. W., Pavan, M. A., and M.V., F. (1989). Use of

gypsum on soils: A review. Adv. Soil Sci. 9, 1-111.

Sharma, P. K., Verma, T., and Gupta, J. (1990). Ameliorating effects of phosphorus, lime and animal manure

on wheat yield and root cation exchange capacity in degraded Alfisols of North-West Himalayas.

Fertilizer Res. 23, 7-13.

Sivaguru, M., and Horst, W. J. (1998). The distal part of the transition zone is the most aluminum-sensitive

apical root zone of maize. Plant Physiol. 116, 155-163.

Somani, L. (1996). “Crop production in acid soils,” 1st edition/Ed. Agrotech Publishing Academy, New

Delhi.

Somani, L., Totawat, K., and Sharma, R. A. (1996). “Liming technology for acid soils,” Agrotech Publishing

Academy, Udaipur, India.

Steiner, C. (2007). Soil charcoal amendments maintain soil fertility and establish carbon sink-research and

prospects. In “Soil Ecology Research Develpments” (T. X. Li, ed.), pp. 1-6. Nova, New York.

Sumner, M. E., and Noble, A. D. (2003). Soil acidification: The world story. In ‘‘Handbook of Soil Acidity’’

(Z. Rengel, Ed.), pp. 1–28. Marcel Dekker, New York.

Tabitha, T. B., Richard, T. K., David, R. H., James, B. H., and Richard, E. R. (2008). Lime effects on soil

acidity, crop yield, and aluminum chemistry in direct-Seeded cropping systems. Soil Sci. Soc. Am. J.

72, 634-640.

Tadesse, G. (2001). Land Degradation: A challenge to Ethiopia. Environ. Manage. 27, 815-824.

Thomas, R. J. (1995). Management of Acid soils (MAS): an interdisciplinary and multi-institutional

collaborative undertaking. In “Proceedings of a DSE/IBSRAM International workshop on soil, water

and nutrient management research”, pp. 71-86. IBSRAM: Bangkok, DSE:Zschortau.

Tisdale, S., Nelson, W., Beaton, J., and Havlin, J. (1993). Soil acidity and basicity. Soil Fertility and Fertilizers,

5th ed. Macmillan, New York, 364-404.

Page 61: SOIL ACIDITY - publication.eiar.gov.et:8080

SOIL ACIDITY MANAGEMENT 54

Tully, K., Sullivan, C., Weil, R., and Sanchez, P. (2015). The state of soil degradation in Sub-Saharan Africa:

Baselines, trajectories, and solutions. Sustainability 7, 6523-6552.

Uchida, R., and Hue, N. (2000). Soil acidity and liming. Plant nutrient management in Hawaiian soils,

approaches for tropical and subtropical agriculture. Edited by JA Silva, and R. Uchida. University of

Hawaii, Honolulu, 101-111.

Vanlauwe, B., Bationo, A., Chianu, J., Giller, K. E., Merckx, R., Mokwunye, U., Ohiokpehai, O., Pypers, P.,

Tabo, R., and Shepherd, K. D. (2010). Integrated soil fertility management: operational definition and

consequences for implementation and dissemination. Outlook Agric. 39, 17-24.

Vanlauwe, B., and Zingore, S. (2011). Integrated soil fertility management: An operational definition and

consequences for implementation and dissemination. Better Crops 95, 4-7.

Velayutham, M. (1980). Problem of phosphate fixation by minerals and soil colloids. Phosphorus Agric.

34, 1-8.

Von Uexküll, H., and Mutert, E. (1995). Global extent, development and economic impact of acid soils.

Plant Soil 171, 1-15.

Walker, D. J., Clemente, R., and Bernal, M. P. (2004). Contrasting effects of manure and compost on soil

pH, heavy metal availability and growth of Chenopodium album L. in a soil contaminated by pyritic

mine waste. Chemosphere 57, 215-224.

Wang, J., Raman, H., Zhang, G., Mendham, N., and Zhou, M. (2006). Aluminium tolerance in barley

(Hordeum vulgare L.): physiological mechanisms, genetics and screening methods. J. Zhejiang

University Sci. 7, 769-787.

Warner, J., Yirga, C., Gameda, S., Rashid, S., and Alemu, D. (2016). Soil Acidity Problems in Ethiopia:

Magnitude, Current Awareness and Practices, and Policy Actions. International Food Policy Research

Institute (IFPRI), Washington, D.C.

Woldeab, A., and Mamo, T. (1991). Soil fertility management studies on wheat in Ethiopia. In “Wheat

Research in Ethiopia: A historical perspective” (H. Geberemariam, D. G. Tanner and M. Huluka,

eds.), pp. 137–172. CIMMYT, Addis Ababa, Ethiopia.

Yamada, T. (2005). The cerrado of Brazil: a success story of production on acid soils. Soil Sci. Plant Nutr.

51, 617-620.

Yirga, C., and Hassan, R. M. (2010). Social costs and incentives for optimal control of soil nutrient depletion

in the central highlands of Ethiopia. Agricultural Systems 103, 153-160.

Zeleke, G., Agegnehu, G., Abera, D., and Rashid, S. (2010). Fertilizer and soil fertility potential in Ethiopia:

Constraints and opportunities for enhancing the system. (I. F. P. R. I. (IFPRI), ed.), pp. 63, Washington,

DC, USA.

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acidic parent material, 6, 14Acidification, 6, 64acid-tolerant, 24Acrisols, 14Active acidity, 21Alisols, 12ammonium fertilizers, 16Amorphous material, 12anions, 23, 28arable soils, 6Base saturation, 14basic cations, 6, 27, 28Basic cations, 6basic elements, 15, 16, 17Biochar, 57bio-logical nutrient management, 70buffer capacity, 19, 38buffer index, 29Calcitic limestone, 28, 41Cambisols, 13, 14carbonic acid, 6, 16, 21clay, 11, 12, 13, 19, 20, 26, 29, 38, 41, 70clay mineralogy, 12, 38Colluvium alluvium, 18correcting acid soils, 47degraded lands, 8, 44desilicated amorphous materials, 12Developing pedo-transfer functions, 70Dolomitic limestone, 28, 41dominant acidic soils, 12Dry spells, 45Dystric, 13Dystric Cambisols, 13

Dystric Nitisols, 13Eutric, 13, 18Eutric Nitisol, 13Exchange acidity, 21exchangeable acidity, 31, 32, 42exchangeable cations, 16, 19, 27, 50exchangeable hydrogen, 6, 19Fluvisols, 12Humic Nitisols, 13hydrated lime, 27, 28, 31Irrigation, 46Kaolinite, 12Latosols, 10leaching, 6, 14, 16, 17, 19, 30, 36, 48, 66lime, 9, 16, 17, 19, 21, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 44, 45, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 59, 60, 62, 63, 65, 66, 67, 71limestone, 13, 16, 27, 28, 30, 39, 45, 53, 54, 65Liming, 27, 39, 48, 50, 59, 62, 63, 64, 67liming materials, 28, 41, 65, 67management of acid soils, 7, 26, 35, 44, 61, 65Mechanization, 46micronutrients, 6, 26, 27, 31, 44, 45microorganisms, 17, 21modeling nutrient flow, 70montmorillonite, 19natural resource management, 8neutralization, 30, 35Nitisol, 7, 13, 18, 31non-calcareous parent materials, 7nutrient dynamics, 70Nutrient management, 70

INDEX

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of nutrient, 24, 70Olivine basalt, 18organic acids, 17, 21, 35, 66organic matter, 6, 8, 13, 16, 17, 19, 26, 30, 35, 36, 42, 44, 45, 57, 58, 65Orthic Acrisols, 13Oxisols, 10, 38, 64P fixation, 10, 22, 31, 35P sorption, 12parent materials, 13, 16phosphate adsorption, 12Phosphate sorption, 23Phosphorus sorption, 12quartz, 15quick lime, 31rate of soil acidification, 59reclamation of acid soils, 8, 51silica, 15Soil acidification, 15, 67soil acidity, 6, 7, 8, 9, 10, 11, 13, 15, 16, 17, 19, 21, 22, 23, 25, 27, 31, 32, 37, 38, 42, 44, 46, 47,

48, 59, 60, 62, 63, 64, 65, 67, 70Soil acidity, 6, 7, 10, 11, 20, 22, 24, 27, 28, 33, 59, 61, 63, 65, 67, 70soil erosion processes, 70soil fertility, 7, 9, 16, 28, 30, 34, 35, 48, 50, 57, 59, 61, 67, 68Soil fertility, 45, 66, 68soil forming factors, 7Soil management and conservation, 45Soil microbiology, 45, 66soil organisms, 22, 57Soil quality, 10Soil reaction, 59Soil restoration, 70source of buffering, 29Trachy-basalt, 18Volcanic ash, 18water-soluble P fertilizers, 12Weathered basalt, 18weathering, 6, 13, 14

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