SOIL ACIDITY

Sandip Patil LA – 9106

Guide: Prof. Deepa Maheshwari Department of Landscape Architecture, CEPT University.

Soil acidity occurs when there is a build up of acid in the soil. The production of acid in the soils is a natural process and many soils in the high rainfall areas are inherently acidic. Acidification is a slow process but it is accelerated by agriculture. As soils become more acidic, plants intolerant of acidic conditions do not thrive and productivity declines. Acid soils are found mainly in the eastern part of the Indo-Gangetic Plain, i.e. in West Bengal, Bangladesh and the mid-hills region of Nepal, where cropping is intensive and monsoonal precipitation is high. In many of these soils, organic matter is also quite low, resulting in poor buffering capacity and low nutrient contents. Causes: Major reasons for soils to become acidic are: • rainfall and leaching, • acidic parent material, • organic matter decay • harvest of high-yielding crops • removal of product from the farm or paddock • inappropriate use of nitrogenous fertilizers Wet climates have a greater potential for acidic soils. In time, excessive rainfall leaches the soil profile's basic elements (calcium, magnesium, sodium, and potassium) that prevent soil acidity. Soils that develop from weathered granite are likely to be more acidic than those developed from shale or limestone. Organic matter decay produces hydrogen ions (H+), which are responsible for acidity (an ion is a positively or negatively charged element). Like that from rainfall, acidic soil development from decaying organic matter is insignificant in the short term. Harvest of high-yielding crops plays the most significant role in increasing soil acidity. During growth, crops absorb basic elements such as calcium, magnesium, and potassium to satisfy their nutritional requirements. As crop yields increase, more of these limelike 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 bermudagrass and alfalfa affects soil acidity more than harvesting grain does. The natural rate of acidification is accelerated by agricultural practices like use of nitrogen fertilizers. The impact of nitrogen fertilisers on acidification depends on the type of fertilizer. • In conditions where rainfall exceeds

evapotranspiration (leaching) during most of the year, the basic soil cations (Ca, Mg, K) are gradually depleted and replaced with cations helds in colloidal soil reserves, leading to soil acidity. Clay soils often contain Fe and hydroxy Al, which affect the retention and availability of fertilizer cations and anions in acidic soils.

• Soil acidification may also occur by addition of hydrogen, due to decomposition of organic matter, acid-forming fertilizers, and exchange of basic cations for H+ by the roots.

Table 1: Soil description based on pH

pH Soil Description

< 5.5 Strongly acid

5.5 - 5.9 Medium acid

6.0 - 6.4 Slightly acid

6.5 - 6.9 Very slightly acid

7.0 Neutral

7.1 - 7.5 Very slightly alkaline

7.6 - 8.0 Slightly alkaline

8.1 - 8.5 Medium alkaline

> 8.5 Strongly alkaline

Source: www.donnan.com

Table 2: Lime required to counteract acidity caused by product removal.

Plant product Lime requirement kg CaCO3 per tonne

Lucerne hay 60 20% subclover/annual grass 15 40% subclover/annual grass 30 60% subclover/annual grass 40 80% submedic/annual grass 50 perennial ryegrass hay 40 cereal hay 22 phalaris/cocksfoot hay 30 wheat grain 5 - 10 Source: Agricultural Bureau of South Australia

Table 3: Acidification rates for different farming systems *in terms of equivalent of kg lime/ha/year required to neutralise acidity

Farming system Acidification rate* Extensive grazing 10-25 Improved pasture 50 Cropping 75-100 Cropping (high N input) 400 Horticulture (high N input) up to 500 Typical hay paddock 300 Lucerne hay 500-600 Source: Agricultural Bureau of South Australia

• Soil acidity is reduced by volatilization and denitrification of nitrogen. Under flooded conditions, the soil pH value increases. In addition, the following nitrate fertilizers -- calcium nitrate, magnesium nitrate, potassium nitrate and sodium nitrate -- also increase the soil pH value.

• Some alkaline soils have Calcium in the form of limestone that is not chemically available to plants. In this case sulfuric acid or Sulfur may be added to reclaim the soil.

Removal of product. Obviously the main aim of any agricultural production system is to produce saleable products. However most agricultural products are slightly alkaline so their removal from a paddock or farm leaves the soil slightly more acidic. The degree of acidification will depend on how alkaline the product is and how many kilograms of product are removed. Where little actual product is removed from the farm, such as in wool production, the system remains largely in balance. The most acidifying forms of agricultural production are operations such as lucerne hay cutting. For instance the removal of one tonne of lucerne hay requires 70 kg of lime to neutralise the resulting acidity. Leaching of nitrogen. Leaching of nitrogen in the nitrate form is a very important factor in soil acidity. Nitrate is a major nutrient for plant growth. It is supplied either from nitrogenous fertilisers or atmospheric nitrogen fixed by legumes. When there is more nitrate than the plant can use, the nitrate is at risk of draining - leaching - below the plants roots and into the ground water system. This leaves the soil more acidic. Leaching of nitrate can happen through inappropriate use of nitrogen fertilisers and is more common in intensive production like horticulture - or because the plants are not at a suitable stage of growth to use the available nitrogen. Pastures based on annual species, the use of long fallow in crop rotations and heavy applications of nitrogen fertilisers are examples of practices that may increase the risk of nitrate leaching. Use of nitrogenous fertilisers. The amount of acid added to the soil by nitrogenous fertilizers varies according to the type of fertiliser. The most acidifying are ammonium sulfate and monoammonium phosphate (MAP), followed by diammonium phosphate (DAP). Less acidifying are urea, ammonium nitrate and anhydrous ammonia. Fertilisers such as sodium and calcium nitrate are not acidifying. Superphosphate has no direct affect on soil pH. However, its application stimulates growth of legumes and clovers which fix nitrogen. This increases the amount of nitrate nitrogen in the soil increasing the potential for leaching and consequent soil acidification. Build-up of organic matter. Over the last 50 years the regular use of fertiliser and improved pastures, particularly subterranean clover, has increased the amount of organic matter in the soil. While organic matter has many beneficial effects including improving soil structure, the increasing amount of organic matter may make the soil more acid. However, organic matter will not build up indefinitely, and when an equilibrium is reached the acidification process stops. It is important to differentiate between a natural build up in organic matter and the build up that occurs by adding organic material from another site. Where organic matter build up occurs due to transported material the increased organic matter generally increases pH (less acid). Rate of Acidification: The rate at which a soil acidifies depends on:- • Soil type: Light sandy soils with little clay or organic matter has lower buffering capacity and therefore

acidity develops more quickly than on heavier soils. • Rainfall: Higher rainfall increases leaching of nutrients which in turn increases acidification. • Land use: Higher production increases the rate of acidification. Shallow rooted plant systems also increase

acidification compared with deep-rooted plants. Soil acidification rates vary according to the agricultural production system in use. Cropping. Product removal and nitrate leaching are usually the most significant factors in a cropping system. Build up of soil organic matter and the use of nitrogenous fertilisers are mostly secondary factors. The relative importance of nitrate leaching will depend on the specific pasture / crop rotation. Use of nitrogenous fertilisers and timing of application will be more important in intensive cropping systems with higher inputs of N fertiliser. Grazing. Nitrate leaching and build up of soil organic matter are the major causes. Product removal in total is usually low and the use of nitrogen fertilisers not applicable. It should be noted that the leaching of nitrate is potentially much less under a perennial pasture than one based on annual species. Horticulture. Much of the acidity in horticulture is localised around micro irrigation outlets. This is where nitrogen is applied via the watering system. Excess use of nitrogen fertiliser, consequent nitrate leaching and product

Table 4: Lime required to counteract acidity caused by fertilizers in acid soils

Acidification (kg lime/kg of fertilizer) Fertiliser minimum maximum average

Anhydrous ammonia 0 3.6 1.8 Urea 0 3.6 1.8 Ammonium nitrate 0 3.6 1.8 Ammonium sulphate 3.6 7.2 5.4 DAP (18:20) 1.8 5.4 3.6 MAP (10:22) 3.6 7.2 5.4 Goldphos (0:18:0:10) 3 Superphosphate nil Muriate of potash nil Source: Agricultural Bureau of South Australia

removal are all major contributors to acidity in horticultural production. Irrespective of the production system the challenge is to manage the causes of acidity to either slow the acidification rate or neutralise the extra acid through the use of a liming material. Symptoms The following symptoms tend to indicate a soil acidity problem: • Reduced yields • Poor plant vigour • Uneven pasture and crop growth (especially acid sensitive plants). • Poor establishment and persistence of pasture species such as lucerne and phalaris where previously they

grew well. • Poor nodulation of legumes. • Stunted root growth. • Persistence of acid-tolerant weeds (eg sorrel and geranium). • Increased incidence diseases • Abnormal leaf colours Effects: • Soil acidity has a negative impact on fertility,

biological activity and plant productivity. • Plant tolerance and productivity • Species and varieties with low tolerance to

acidity will decline in productivity and persistence. Greater reliance is placed on acid tolerant plants that are generally not as productive.

• Soil fertility • Soil pH influences nutrient availability. In

strongly acid soils, potassium, calcium and magnesium are depleted due to leaching. Low levels of calcium and magnesium can also cause stock health problems such as milk fever and grass tetany. A lack of calcium can cause soil structural problems.

• Aluminium, if present in the soil, becomes available once pH(CaCl2) goes down to less than 5. Aluminium is toxic to plants and severely restricts root growth. Acids attack soil minerals and increase net loss of nutrients from the soil eg. Mn, Cu, Zn.

• In some soils Manganese toxicity will develop around pH (CaCl2) 5.0 although this is unusual in most high rainfall SA soils

Effects on Biological activity Soil acidity reduces and even stops the activity and survival of useful soil organisms such as: • nitrogen fixers • decomposers • nutrient recyclers • Organic mats often form on the soil

surface as a result of reduced biological activity and organic matter not being broken down.

• Soil Structure/Clay Degradation • The leaching of nutrients and increased

availability of clay minerals such as Al and Fe can result in a decline in soil structure and some irreversible damage to the clay content of soil.

• As a result of poor pastures, limited growth and shallow root depth, recharge under acid soils is greater than under productive perennial pastures. This will contribute to rising water tables and an increase in the salinity of streams and dryland salinity.

Table 5: Effects of acidic soil on plant nutrients Nutrient Action Outcome Potassium Depleted by leaching health problems Calcium Depleted by leaching Poor soil structure Magnesium Depleted by leaching Poor soil structure Phosphorus Molybdenum

Deficiency byfixation Poor pasture growth

Aluminium Excess Toxic to plants if soil reserves are high

Iron Excess Ties up other nutrients eg P

Source: Agricultural Bureau of South Australia

Availability of nutrients at various pH values Acid - Neutral Alkali - 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10nitrogen, N phosphorus, P potassium, K calcium, Ca magnesium, Mg sulfur, S iron, Fe manganese, Mn boron, B copper, Cu zinc, Zn

• Streams are also more likely to contain nutrients leached out of the soil due to the acidic conditions. Soil pH Soil pH is an indication of the alkalinity or acidity of soil. It is based on the measurement of pH, which is based in turn on the activity of hydrogen ions (H+) in a water or salt solution. When in balance (pH 7) the soil is said to be neutral. The pH scale covers a continuum ranging from 0 (very acidic) to 14 (very alkaline or basic). pH scale being logarithmic, a ph difference of 1 is a difference of 10 times. E.g. pH 5 soils are ten times more acidic than pH 6 soils. It is however uncommon to find soils at either extreme of range. Under many conditions soils tend to become more acid or alkaline over time if steps are not taken to maintain a balance. Soil pH is an important consideration for several reasons; including the fact that many plants and soil life forms prefer either alkaline or acidic conditions, that some diseases tend to thrive when the soil is alkaline or acidic, and that the pH can affect the availability of nutrients in the soil. Soil pH affects the availability of soil constituents to plants and soil micro-organisms. For most plants, the ideal soil pH (water) test result is pH 6 - 7.5, although many will tolerate pH 5.5 - 8.5. However, the tolerance to extremes in pH varies between plant species and within species. Therefore, consideration of the need for soil amelioration will depend on individual circumstances. The correct pH depends on the crop being produced. 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 calcium and perform best between pH 6.5 and 7.5: pH 6.0 to 7.0 is best for nutrient availability. Nutrient availability in relation to soil pH The majority of food crops prefer a neutral or slightly acidic soil. Some plants however prefer more acidic (e.g., potatoes, strawberries) or alkaline (brassicas) conditions. • During the acidification process the decrease in pH result in a release of positively charged ions (cations) from

the cation exchange surfaces (organic matter and clay minerals). In the short term acidification thus increases the concentration of potassium (K), magnesium (Mg), and calcium (Ca) in soil solution.

• Once the cation exchange surface has become depleted of these ions, concentration in soil solution can be quite low and is largely determined by the weathering rate. The weathering rate in turn is dependent on presence of easily weathered minerals, surface area, soil texture, soil moisture, pH, concentration of base cations such as Ca, Mg and K as well as concentration of Aluminium.

• The amount of plant available nutrients is a much more difficult issue than soil solution concentrations. The term plant available nutrients usually include pools other than soil solution but which are supposed to replenish soil solution pretty fast e.g. through cation exchange. One reason for including such pools is the plants capability of releasing organic acids which increase the total soil solution concentration of some cation nutrients that are important for the plant.

• There is a complex relation between soil solution concentration of Ca, Mg and K and reasonable pH-values, because Ca, Mg and K are base cations, i.e. cations of strong bases and strong bases are fully dissociated at the pH-ranges occurring in most natural waters.

• Mineral weathering increases pH by releasing Ca, Mg and K. Soil rich in easily weatherable minerals tends to have both a higher pH and higher soil solution concentration of Ca, Mg and K.

• Deposition of sulphate, nitrate and to some extent ammonia decrease pH of soil solution essentially without affecting Ca, Mg and K concentrations whereas deposition of sea-salt increases Ca, Mg and K concentrations without having much of an effect on soil solution pH.

• Soil solution can be extracted from the soil in many ways, e.g. by lysimeters, zero-tension lysimeters, centrifugation, extraction with CaCl2, overhead shaking of soil sample with added water, etc.

• Many nutrient cations such as zinc (Zn2+), aluminium (Al3+), iron (Fe2+), copper (Cu2+), cobalt (Co2+), and manganese (Mn2+) are soluble and available for uptake by plants below pH 5.0, although their availability can be excessive and thus toxic in more acidic conditions. In more alkaline conditions they are less available, and symptoms of nutrient defficiency may result, including thin plant stems, yellowing (chlorosis) or mottling of leaves, and slow or stunted growth.

• pH levels also affect the complex interactions among soil chemicals. Phosphorus (P) for example requires a pH between 6.0 and 7.0 and becomes chemically immobile outside this range, forming insoluble compounds with iron (Fe) and aluminium (Al) in acid soils and with calcium (Ca) in calcareous soils.

Soil life and pH A pH level of around 6.3-6.8 is also the optimum range preferred by most soil bacteria, although fungi, molds, and anaerobic bacteria have a broader tolerance and tends to multiply at lower pH values. Hence, more acidic soils tend to be susceptible to souring and putrefaction, rather than undergoing the sweet decay processes associated with a healthy, living soil. Earthworms, whose feeding and tunnelling activities aerate the soil and speed the decay of organic matter, immeasurably benefitting the soil, also prefer these near-neutral conditions.

pH and plant diseases Many plant diseases are caused or exacerbated by extremes of pH, sometimes because this makes essential nutrients unavailable to crops or because the soil itself is unhealthy. For example, chlorosis of leaf vegetables and potato scab occur in overly alkaline conditions, and acidic soils can cause clubroot in brassicas. Determining pH pH is not constant in soil or water, but varies on a seasonal or even daily basis due to factors such as rainfall, biological growth within the soil, and temperature changes. Rather, a map of the pH level is a mosaic, varying according to soil crumb structure, on the surface of colloids, and at microsites. The pH also exhibits vertical gradients, tending to be more acidic in surface mulches and alkaline where evaporation, wormcasts, and capillary action draw bases up to the soil surface. It also varys on a macro level depending on factors such as slope, rocks, and vegetation type. Therefore the pH should be measured regularly and at various points within the land in question. Methods of determining pH include: • Two common ways of measuring soil pH are in water and in calcium chloride. The latter is preferred for acidic

sols because results are generally more consistent. pH measured in calcium chloride are generally 0.5 to 1 pH unit lower than if it is measured in water.

• Observation of predominant flora, especially Calcifuge plants (those that prefer an acidic soil). Observation of symptoms that might indicate acidic or alkaline conditions, such as occurrence of the plant diseases mentioned above or salinisation of alkaline soils.

• Use of litmus paper. A small sample of soil is mixed with distilled water, into which a strip of litmus paper is inserted. If the soil is acid the paper turns red, if alkaline, blue.

• Use of a commercially available electronic pH meter, in which a rod is inserted into moistened soil and measures the concentration of hydrogen ions.

• It is essential to take into account the method by which pH has been measured. Depending on whether or not the water has been equilibrated with ambient CO2 pressure or not the pH reported from the same site may be either high or low.

• This is because the carbon dioxide pressure deep down in the soil might be 10–20 times higher than the ambient pressure due to decomposition of organic material. The higher carbon dioxide pressure results in more carbonic acid and hence a lower pH.

Acidity Management • Apply liming material at a rate based on pH, soil type, land use • Use acid-tolerant plants. This is a short term option only as the soil continues to acidify with associated

consequences. • Reduce the rate of acidification to a minimum. • Sow perennial pasture - deep rooted, more summer active, reduce N leaching. • Use fertilisers wisely - match plant requirements, monitor plant and soil levels, and use least acidifying N

fertilisers. • Feed hay onto paddock in which it was cut where possible - recycles nutrients and alkalinity. • Rotate grazing paddocks. Altering soil pH The aim when attempting to adjust soil acidity is not so much to neutralise the pH as to replace lost cation nutrients, particularly calcium. This can be achieved by adding limestone to the soil, which is available in various forms: Liming • Agricultural lime (ground limestone or chalk).It is

slow reacting, thus its effect on soil fertility and plant growth is steady and long lasting. Ground lime should be applied to clay and heavy soils at a rate of about 500 to 1,000 g/m² . As lime dissolves in the soil, calcium (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 (has a higher pH).

• Quicklime and slaked lime. The former is produced by burning rock limestone in kilns. Being highly caustic, it cannot be applied directly to the soil. Quicklime reacts with water to produce slaked, or hydrated, lime, thus quicklime is spread around agricultural land in heaps to absorb rain and

atmospheric moisture and form slaked lime, which is then spread on the soil. Quicklime should be applied to heavy clays at a rate of about 400 to 500 g/m², hydrated lime at 250 to 500 g/m².

• Coarse textured soils (eg. sands) need less lime than finer textured soils. Also, low organic matter soils need less lime than peaty soils. A lime requirement test will incorporate these affects when used to determine the amount of lime needed to raise soil pH. Other factors needed to determine an appropriate lime rate include target pH of the specific plant, lime quality, application method and economics.

• 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. The more calcium carbonate and the finer the material size, the higher the ECCE. Because the ECCE of lime is not always 100 percent, the amount of material required to provide that percentage must be calculated:

ECCE lime required x 100 = lime required ECCE % • It takes water to activate the lime reaction, so lime works slowly in dry soil. 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. Test soil periodically when growing high-yielding perennial forages to identify lime deficiency early enough to change the pH with unincorporated broadcast applications.

Economics: Research data shows that responses to lime can be profitable. Most economic advantage is achieved by liming highly productive or perennial pastures. • Perennial pasture: phalaris/subclover. Most economic rate is 3.5t/ha, which is sufficient to increase subsoil pH. • Annual pasture: annual ryegrass/subclover. Most economic rate is 1.5t/ha, but is insufficient to improve subsoil

acidity. Benefits of liming • Raises soil pH. • A well balanced soil pH is important for: soil fertility and nutrient availability plant species that can be grown

biological activity of the soil • Pasture vigour and productivity • Lime application increases pasture productivity. Trials throughout the Mt Lofty Ranges showed increases in

productivity up to 35%. • Livestock health • Increased calcium and magnesium levels in the plant helps to overcome problems such as grass tetany in

cattle. • Maintaining a favorable pH is extremely important in a soil fertility management plan. Routine soil testing

reveals soil pH levels and provides liming recommendations. All too often, producers lose forage production by ignoring lime deficiency in soils with acidity problems.

Calcium sulfate, known as gypsum can be used to amend soil acidity and is also useful for lightning the structure of heavy clays. The pH of an alkaline soil is also lowered by adding sulfur, iron sulfate or aluminum sulfate, although these tend to be expensive, and the effects short term. Urea, urea phosphate, ammonium nitrate, ammonium phosphates,

ammonium sulfate and monopotassium phosphate also lower soil pH. As acidity is a slow process and the correction of acidity by liming is also slow where possible soils need to be limed before acidity is having an effect. Cut Buffering The most important source of buffering in an acidic soil is the exchange of the limelike 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. In time, reserve elements are depleted enough to cause acidity. When you apply lime, consider the size of the reservoir or buffering capacity. Typically, clay soils have a larger reservoir than sandy ones, which means that they require more lime to achieve a favorable pH. Pay attention 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 remeasuring pH, the buffer pH is larger when the reservoir is small (table 1). If

Table 6: ECCE* Lime required (tones) Buffer index pH 6.8 pH 6.4

>7.1 none none 7.1 0.5 none 7.0 0.7 none 6.9 1.0 none 6.8 1.2 0.7 6.7 1.4 1.2 6.6 1.9 1.7 6.5 2.5 2.2 6.4 3.1 2.7 6.3 3.7 3.2 6.2 4.2 3.7

the buffer pH is 6.8, then it will take 1.2 tons of effective calcium carbonate equivalents (ECCE) of lime to raise the pH to 6.8 and 0.7 ton to increase it to 6.4. Soil Acidity in India: Acid soils are estimated at more than 800 million hectares world wide. In India, it is about 100 million hectares of the total geoghraphical area. State wise area of Acid Soil Regions (ASR) is given in table below. More than 80% of the cultivable lands in the ASR are rainfed and there is wide variation in the total annual rainfall and its distribution in different agroclimatic zones. The cropping system under rainfed conditions depends upon rainfall distribution, the total rainfall and the moistures storage capacity of the soil. Among the 8 broad soil groups in Orissa, the laterites and lateritic soils, red soils, mixed red and yellow soils, mixed red and black soils and brown forest soils are generally acidic in reaction. The upland soils of sedimentary nature are also acidic because of the presence of excess soluble sulphates and chlorides. Acid soils are more concentrated in the inland districts rather than the coastal plains. There is a wide variation in pH are seen within the same groups of acid soils. The pH of lateritic soils from various regions of Orissa ranged from 4.2 to 6.7 and that of red soils from 4.5 to 6.5. The mixed red and black soils of Nayagarh are relatively more acidic (pH 4.7 to 5.2). Brown forest soils are mildly acidic (pH 6.3 to 6.5).

Table 7: Acid Soil Regions (ASR) in India (*Area in million hectares)

Sl. No.

Name of the State Total Area* Area under acid soil*

Percentage of Total Area %

1 Assam & N.E. States 25.0 20.0 80

2 West Bengal 8.8 3.5 40

3 Bihar & Jharkhand 17.4 5.2 33

4 Orissa 15.6 12.5 80

5 Madhya Pradesh & Chhatisgarh 44.3 8.9 20

6 Andhra Pradesh 27.7 5.5 20

7 Tamil Nadu 13.0 2.6 20

8 Karnataka 19.2 9.6 50

9 Kerala 3.9 3.5 90

10 Maharashtra 30.8 3.1 10

11 Uttar Pradesh 29.4 2.9 10

12 Himachal Pradesh 5.6 5.0 90

13 Jammu & Kashmir 22.2 15.5 70

Cropping Systems for Acid Soil Region : Traditionally, farmers of Acid Soil Regions (ASR) have been growing rice irrespective of the type of land (Upland, Medium land & low land). Rice has certain amount of tolerance to soil acidity; and flooding of the field also creates favourable condition (increase in pH and availability of P, Si and K) for growth of rice. Liming is desirable for raising the productivity of several crops. The acid sensitive crops like cotton, soybean, groundnut, french bean, pigeon pea etc. are better adaptable to acid soils with proper liming. Crops are classified according to their relative response to liming. This information can be utilised in fixing suitable cropping sequence. Under rainfed conditions, highly responsive crops like cotton, soybean, pigeon pea etc. may be grown in the first year of liming, followed by medium response crops like maize and wheat in the subsequent seasons. The low responsive crops like millets, rice, barley, linsed etc. may be grown when the effect of liming has been further reduced. Soil erosion and shifting cultivation are major problems in hilly-tracts of ASR. Agri-horticultural and agro forestry systems need to be introduced in such tracts. In general, regions receiving more than 900 mm rainfall and with a moisture storage capacity of 200 mm in the root zone, double cropping can be taken up.

Cropping pattern (a) Rainfed Areas Type of land Crops Inter cropping / sequence cropping

Higher elevation Mesta, Pigeonpea, Maize, Groundnut Inter cropping of pigeonpea + Groundnut

Medium land Finger millet, Rice (Short duration) Rice, Finger millet, Maize Horsegram, Cowpea

Low Rice Rice-Pulse, Rice-Rapeseed (b) Irrigated Area

Kharif Rabi Summer Rice Cabbage Lady's finger Green pea Rice Rice Rice Tomato Cowpea

Medium land (BBSR)

Rice Potato Lady's finger Rice Groundnut - Rice Green pea Rice Chiplima (Medium land) Green pea Rice Rice

Table 8: Lime Required to raise pH to 6.5 (kg/ha)

Soil Type Sl. No.

pH Range

Sandy Sandy loam Loam Silt loam Clay & loamy clay

1 4.5 to 5.0 (For pure CaCo3) 4250 7250 10750 15000 20000

Equivalent quantity of paper mill sludge

5600 9600

Average

14300

15220

20000

15 ton

26600

2 5.1 to 5.5 (Pure CaCo3) 2500 4250 6250 8500 11300

Equivalent quantity of paper mill sludge

3300 5600

Average

8300

8700

11300

8.5 ton

15000

3 5.6 to 6.0 (pure CaCo3) 1000 1750 2500 3500 5000

Equivalent quantity of paper mill sludge

1300 2300

Average

3300

3620 Kg.

4600

3.5 ton

6600

Bibliography: • Indian Agricultural Research Institute, www.iari.org • Indian Council of Agricultural Research publications • Agricultural Bureau of South Australia, www.bettersoils.com.au • www.wikipedia.com • www.donnan.com • Department of Primary Industries, Victoria, Australia, www.dpi.vic.gov.au • Noble Foundation, www.noble.org • State of the Environment, Report for South Australia, www.dwlbc.sa.gov.au • Stephan Hunger, Soil Acidity & Leaching, ebook • NSW Government Leaflet, Acid soil action initiative