IPADS Soil Fertility Management(2) Soil Acidity, Liming and Alkalinity

Department of Global Agricultural SciencesIPADS

Kensuke OKADA(akokada@mail.ecc.u‐tokyo.ac.jp)

1

(Llanos Orientales in Colombia, (KO)

International Program in Agricultural Development Studies (IPADS)18 January 2016

Soil acidity --- one of the major soil chemical constraints

Introduction : Problems of soil acidity in the field

• For example, if you are working in the humid tropics,

• And the color of the soils are red or yellow,

• The crops are the maize, sorghum, wheat, barley, soybean, cotton, etc.

• Even if you apply enough amount ot fertilizers, the yield is still low,

• You observe the roots are not growing normally

→ Then, the soil acidity would be the root‐cause problem

How to solve the problem?• Then you can measure the pH• Once the pH is low enough, you would think of applying lime to increase pH.

• You can do it for pots, but for the field......

• How much lime should you apply?  How to calculate?

• If you have 2000 ha of land, can you still apply?

→Therefore we need more knowledge to correct acid soils problems in feasible ways

Today’s topic1. Geographical distribution of acid soils in the world2. How do the soils become acidic?3. The problem of acid soils, how to measure4. Plant’s Response to Soil Acidity5. Solution to the soil acidity

5‐1. Lime application5‐2.  Selection and breeding of acid‐soil tolerant species and varieties

5

1. GEOGRAPHIC DISTRIBUTION OF ACIDIC SOILS IN THE WORLD

6

1. Geographic Distribution of Acidic Soils in the World

Severe AcidSoils (31%)

LessProble-maticAcid Soils(11%)

Percentage of acid soils, inthe land (agriculture possible) in the world

South America

(27%)Africa(27%)

Other region

Regional Distribution ofSevere Acid Soils

Strongly acidic soils in the world

Acrisols

Podsols

‘Acidic’ Histsols

‘Acidic’ Andosols

Arenosols

Sub‐humid savannas in South AmericaLlanos in Colombia andVenezuela

Cerrados in Brazil

10

Eastern plain of Colombia(Llanos Orientales)

Western plain of Venezuela

Amazon

Cerrados

Savannas and tropical rain forest in South America

11Cerrados in Brazil

Savanna landscape with trees having twisted trunks and branches

Tropical sub-humid savanna (Llanos Orientales, Colombia, S.A.)

13

Native grassland in Llanos

Regular fire

Grazing

Native pasture in Llanos Orientales, Colombia

Characteristics of the soil at eastern savannas of Colombia (Llanos Orientales).

(ICA, La Libertad, 0‐20 cm, Mar. 1993)

Texture (%)Sand Silt Clay

44 17 39

Micro Nutrient (ppm)B Zn Mn Cu Fe

0.07 0.18 4.97 0.29 35.07

Exchangeable Cations (meq/100g soil)Al Ca Mg K Al sat. (%)

3.08 0.23 0.06 0.08 91.4

O.M.(%) pH (1:1 w) P (ppm-P, Bray)

3.4 4.8 6.0

2. HOW DO THE SOILS BECOME ACIDIC?

16

Cause of natural soil acidification in humid climate

1. Theoretically rain water is acid (pH=5.6) because it is saturated with CO2 in the atmosphere. 

2. In the region where the rainfall exceeds evaporation, the proton (H+) in the water displaces the cations on the surface of the soil colloids.

3. Then the cations are leached. 4. The remaining H+ destroyed part of the clay mineral 

which consists of Al‐Si‐Fe and liberate them. 5. Al3+, due to its selective adsorption, displaces H+ and 

become the major exchangeable cation in the acid soils. 6. If the acidification proceeds, the clay minerals are further 

destroyed and more Al3+ will exists in the soil solution.

Cause of natural soil acidification in humid climate

Ca

CaCaMg

HMgK K

Ca2+Mg2+

K+

H+H+

H+

H+H+H+

Mg2+Ca2+

Ca H

K

H

H

HH

H

Rain(pH=5.6)due to CO2

Leaching of cations to sub soil or under water

Ca H

K

H

H

HH

H

Al3+

Al3+AlAlAl

Al

Al3+Al3+

Al3+

H+

H+

H+

H+

Structure of clay minerals (eg. kaolinite)

Al and Si are in the core of the clay mineral

Additional soil acidification mechanisms

• Ammonium fertilizer application and organic matter decompositionacidify the soils through nitrification

NH4+ + 2O2  →  NO3

‐ + 2H+ + H2O• Acid rain caused by petroleum combustion

NO2 + H2O  →  HNO3 (nitric acid) SO2 + H2O  →  H2SO4 (sulfuric acid)

• Uptake of cations (Ca2+, Mg2+, K) by plants and N2‐fixation produces H+

Effect of fertilizers on pH change21

(Okada et al. 2001)

3. THE PROBLEMS OF ACID SOILS, HOW TO MEASURE

22

Soil Acidity ‐‐‐ “Complex Syndrome”

Low pH

High Al (exch‐Al, soil solution Al)

Solution Al ‐‐ (Al3+, Al(OH)x, Al13, Complexed, Polymeric, etc)

Low Ca (exch‐Ca, soil solution Ca)

Ratio of Ca/Al, etc

Low Mg, K, and other cations

Low P

Criteria for Soil Acidity

Soil pHtable,  pH buffer curve

Soil acidity1M NaCl, 1M KCl, SMP, double buffer

Alexch‐Al,Al saturation=(exch‐Al)/

(exch‐Al, H, Ca, Mg, K)x 100

flat and level field field with some gradient

eg. slope, gradient of soil moisture

An example to collect 5 samples per field (less than 0.5 ha, depending on the heterogeneity of the field)

2. Carry the small bucket andput the samples into the bucket

1. Collect the samples at 5 points carrying small bucket

3. Mix the sample well and make a composite sample. Then take out the necessary quantity for the analysis and put it into the plastic or paper bag and take to the laboratory. Discard the remaining soils back to the field.

Soil core and other necessary tools1. Case for soil core 2.Soil core (100 mL) 3. Cap for core4. Tool to insert soil core into the soil (for soft soils)5. ibid. (for hard soils, hit by hammer)6. ibid. (for paddy surface soil)7. Knife to cut the soil surface after collection8. Hand shovel 9. Scissors to cut vinyl tape 10. Scale 11. Vinyl tape to seal the core after capping 12. Cloth for cleaning core after collection13. Brush and spatula 14. Hammer (underlined are the special tools for this purpose)

Tools for collecting soil samples

(Standard Methodsfor Soil Analysis, Hakuyuusha, 1986 in Japanese)

Simpler tools for soil sample collection

Simpler method to collect soils for diagnosis

Soil surface

Sub soil

Surface soil(cultivated depth (ca. 10-15 c

(2) Collect soil along the side surface of the V-shapehole using hand shovel or spatula

(1) Firstly make V-shape hole up to the depth of the cultivation by hand shovel

= very important factor

• pH < 4        free acid  (H+)• pH < 5.5     exchangeable Al3+

• pH   7.8‐8.2   CaCO3

• (in water  suspension)

3‐1 Soil pH

Method to measure soil pH1. Take each 10 g of dried soil or fresh soil (eq. 10g in 

d.w.) in a series of 50 mL plastic beakers.2. (The dried soil sample should be prepared air‐dried 

with room temperature or less than 40℃, and passed through 2 mm sieve.)

3. Add 25 mL (1:2.5) or 10 mL (1:1) of distilled water to each beaker and stir them well with glass rod. 

4. Wait for 30‐60 min.5. Again stir with glass rod.6. Insert the glass‐electrode into a soil suspension. Wait 

around 30 sec to obtain stabilized reading.7. Then repeat 5 and 6 for the next beaker. The electrode 

may not be washed each time. (When the soil contains higher amount of organic matter 

of clay, 1 to 2.5 ratio is recommended. )

pH measurement in the field

Prepare  (1) Small plastic bags with zip, (2) Distilled water, and (3) Spoon1. Take some amount of soil 

sample using spoon and put it into the plastic bag and add distilled water (soil : water = ca. 1:2). 

2. Zip and shake well and keep it for some minutes.

3. Pour the soil suspension into the well of the portable pH meter and read.

Portable pH meterUS$ 200-300

Different methods of measuring soil pH

• Water : Soil = 2.5 : 1  (mainly Europe, Japan)• Water : Soil = 1 : 1  (mainly US)

Effective and highly acidic soils eg. Oxisols

• 0.01 M CaCl2 (mainly US) Slightly more acidic but stable and easy to measure

• 1N KClThe value is more acidic, measuring Al3+ also. 

32

Effective CEC and Al saturation• Effective CEC (ECEC)=sum of the exchangeable cations (Ca, 

Mg, K, Na, Al)• Aluminum saturation (%) = 

exch‐Al / ECEC x 100Ca

Mg

H

K

AlAl

Al

Al

3‐2 Exchangeable Al

Why effective CEC is better than CEC measured at pH 7 (variable charge)

34

Influence of pH on CEC in pure OM and montmorillonite clay mineral

35

Alminum saturation and soil pH 36

Base saturation and soil pH37

Method to measure exchangeable Al by KCl extraction

Reagents1.1N KCl solution (74.56 g of KCl / L)2.Aluminum complexing solution, 1N KF3.HCl,   0.1 N4.NaOH,  0.1 N5.Phenolphthalein solution (1g of phenolphthalein / 100 mL of ethanol)

Procedure1. To a 10 g soil, add 25 mL of 1N KCl solution, mix and 

let stand for 30 min. 2. Filtrate it with adding additional 125 mL of 1N KCl 

solution.3. Add 4‐5 drops of phenolphthalein and titrate with 

0.1 N NaOH to the first pink endpoint. Correct for a blank with 150 mL KCl solution. 

4. Record the titer for NaOH, add 10 mL of 1N KF, and titrate with 0.1 N HCl until pink color disappears. Wait for 30 min, and add additional HCl to a clear endpoint.

Calculation

• [acidity (meq)] = (NaOH sample (mL) – NaOH blank (mL)) ×N ×100 / (sample weight (g))

• [exchangeable Al (meq)] = (HCl (mL)×N×100) / (sample wt. (g))

• H+ (meq) = acidity – exchangeable Al 

Measurement of exchangeable cations

1. Take 5 g of air‐dried soil sample in 250 mL plastic bottle.

2. Add 100 mL of 1M ammonium acetate (pH 7.0) and shake for 1 hour.

3. Filtrate and measure the content of Ca, Mg, K, Na, Al by atomic absorption, ICP, ion electrode, colorimetry.

A simple equipment for extracting soil solution by centrifuge

3‐3 Soil solution Al3+

Relationship between pH and the distribution and average charge of soluble Al species

43

4. PLANTS RESPONSE TO SOIL ACIDITY

44

Differential effects of Al3+ on the root 

growth of Al tolerant and susceptible soybean varieties

45

var. Perry

var. Chief

0 8 12 (ppm Al3+)

(Solution culture containing 2 ppm of 

Ca (Foy et al) )

Root elongation: the most sensitive criteria for 

acid‐soil tolerance

Zone of cell elongation : site of action of Al

Relative tap root length of soybean as affected by Al3+ in solution. 

48

Taproot lengths were measured after four days of growth and compared with root elongation in zero Al+3treatments. 

Effect on wheat grain yield49

(Patiram et al, 1990. J. Ind. Soil Sci. 38:719-722)

Effect of Al in solution on rice varieties in solution culture experiment

5 SOLUTION TO THE SOIL ACIDITY

51

An example to calculate necessary lime application rate for an acid soil

(dry soil 10 g)

5‐1 Lime application

Methods to decide the necessary amount of lime to be applied (lime‐buffer method)    1.

1. Take air‐dried and sieved soil, equivalent to 10 g (oven‐dry),  and put it into the plastic or glass bottle of 50 mL. 

2. Add calcium carbonate (CaCO3) powder at 0, 10, 25, 50, 75, 100 mg and distilled water at 25 mL to each bottle.

3. Swirl well and keep it still for 24 hr at room temperature. 4. Then keep it for further 5 hr with occasional swirling.5. Gently pass the air from air compressor at the rate of ca. 2 L per 

minute and bubble the suspension for 2 min, with small pipette at the end of the air tube to discharge excess CO2.

6. Immediately after passing the air, measure the pH, and make the lime‐pH curve as in the figure. 

7. From the figure, it can be read that you need to add 40 mg CaCO3per 10 g soil if you want to raise the pH from 5.0 to 6.0.

8. The necessary quantity of lime to be applied in the field (X kg/ha) can be calculated as follow:

X = { 10000 (m2) × d (cm) / 100 × b } × x (mg) / 10 = d× b× x× 10

where b is bulk density of the soil (kg / L) and the depth to be corrected is d (cm) and x is the amount of CaCO3 necessary to be added (CaCO3 mg / 10g soil). 

9. If x is 40 (mg/10g soil), bulk density is 1.2 and depth 0‐15 cm should be corrected, the amount of lime needed is    15 x 1.2 x 40 x 10 = 7,200 kg / ha = 7.2 t CaCO3 / ha

10.CaCO3 has the 56 % alkalinity. Each commercial lime has the indication of their alkalinity. If  the lime you use has the label indicating its alkalinity as 53 %, then the application rate of the lime can be calculated as : 7.2 (t) ×56 (%) / 53 (%) = 7.6 (t/ha)

11. The soil should be mixed well to the depth planned with rotary or drive harrow.  

*Precise planning of the depth to be applied lime is important. If the amount is based on 15 cm and only 10 cm is mixed, it is over‐limed. 

Different Liming Materials and their Calcium Carbonate Equivalence (CCE) 

(Mahler, R. L.)

Various Liming Materials

Limestone Powered Limestone Granulated Limestone

Dolomite

Powered Limestone

Guaranteed alkalinity=72.0

Particle size and the effectiveness of liming materials

Larger the particle size (smaller the mesh), smaller the pH correcting ability and effectiveness.

Lime Sower

Spreader

Rotavator to incorporate lime into the soil

Routine methods for lime requirement measurement

• Shemaker, McLean and Pratt (SMP) single‐buffer method

• Woodruff single buffer • Mehlich single‐buffer • Adams and Evans single‐b• Yuan double‐buffer• SMP double‐buffer

• Based on Exchangeable‐Aluminum Level(neutralize ex‐Al)

61

5‐2 Genetic improvement• Why is this knowledge important?• Genetic improvement is usually carried out by the breeders.• But they need the collaboration with soil scientists, plant nutrient 

specialists and plant physiologists. • The essential areas for the contributions are : 

(1) site selection / screening conditions, (2) rapid and accurate screening technologies, (3) physiological mechanisms. 

• Tolerance/Resistance vs. Potential productivity• Use of Inter/Intra specific difference

The range of aluminum tolerance in field crops. (Adapted from TropSoils 1991)

Tolerance to Al (% Al sat.)

Low(0-40)

Moderate(40-70)

High(70-100)

FIELD CROPS

Maize ●

Soybean ● ●

Sorghum ● ●

Millet ● ●

Groundnut ●

Rice ● ●

Cassava ●

Cowpea ●

Bean ● ●

Mungbean ●

Wheat ● ●

Cotton ●

Tolerance to Al (% Al sat.)

Low(0-40)

Moderate(40-70)

High(70-100)

FORAGE GRASSES

Brachiaria spp. ●

Andropogon spp. ●

Panicum spp. ● ●

FORAGE LEGUMES

Centrosema spp. ●

Stylosanthes spp. ●

Kudzu ●

Mucuna ● ●

Crotalaria spp. ●

TREES

Leucaena spp. ●

Rubber ● ●

Cocoa ●

Oil palm ● ●

5‐2 (a) Selection of suitable species

Brachiaria humidicola

Forage grasses and legumes evaluated in RIEPT and released as cultivars.Species CIAT

No.Cultivar Name

Yr. of release

Country

GRASSESAndropogon gayanus

621 Carimagua 1

1980 Colombia

Planaltina 1980 BrazilSabanero 1983 VenezuelaVeranero ---- PanamaSan Martín 1984 PeruLlanero 1986 MexicoAndropogon 1988 Cuba

Veranero 1989 Costa RicaOtoñero 1989 HondurasGamba 1989 Nicaragua

Brachiaria dictyoneura

6133 Llanero 1987 Colombia

Brachiaria brizantha

26646 La Libertad 1987 Colombia

6780 Brizantha 1987 CubaGigante 1989 VenezuelaInsurgente 1989 Mexico

Brachiaria 606 Brachiaria 86-87 Cubadecumbens Chontalpo 1989 Mexico

Señal 1989 Panama

Pasto Peludo 1991 Costa Rica

Brachiaria 679 Aguja 1989 Venezuelahumidicola Humidicola 1989 Panama

Chetumal 1990 MexicoHumidicola 1992 Colombia

Panicum 661 Vencedor 1990 Brazilmaximum Tanzania-1 1990 Brazil

LEGUMESStylosanthes capitata

10280 Capica 1983 Colombia

S. guianensis var. pauciflora

2243 Bandeirante 1983 Brazil

S. macrocephala 1281 Pioneiro 1983 BrazilS. guinensis 184 Pucallpa 1985 Peruvar. vulgaris Zhuhauco 1987 ChinaCentrosema acutifolium

5277 Vichada 1987 Colombia

Clitoria ternata --- Thehuana 1988 MexicoClitoria 1990 Honduras

Pueraria phaseoloides

9900 Jarocha 1989 Brazil

Desmodium ovalifolium

350 Itabela 1989 Brazil

Centrosema pubescens

438 Centrosema perenne

1990 Hundurals

Arachis pintoi 17434 Amarillo 1990 AustraliaManíforrajero Perenne

1992 Colombia

$45

$35$35

$35

http://www.ciat.cgiar.org/catalogue/index.htm

pH LOW --------------------------- HIGHAl HIGH -------------------------- LOWCa LOW -------------------------- HIGH

Effect of lime application on the soil chemical characteristics and the response of acid‐soil tolerant and susceptible crops

5‐2 (b) Breeding for tolerant varieties

STRESS TOLERANCE(Y-axis),

YIELD POTENTIAL(X-axis),

and CHOICE OFVARIETY

Site selection: Yield with and without stress

50.00

60.00

70.00

80.00

90.00

100.00

110.00

120.00

1 2 3 4 5

Yield on acid soil

(Yield on acid soil)/ (Yield on non-acid soil) * 100

Acid‐soil tolerant varieties

(Valencia and Leal, 2004

Acid‐soil tolerant varieties for soybean and sorghum

(Valencia and Leal, 2004)

SoybeanSorghum

Response of acid‐soil tolerant maize variety to Al saturation and phosphorus application

Sikuani : new variety tolerant to acidic soils(developed by CIMMYT)

Acid‐soil resistant maize: SA3 (Sikuani)

Oryzica Sabana 6, a high-yielding variety of upland rice adapted to acid soil savannas, released in 1991 in Colombia

Oryzica Sabana 6 Oryzica Sabana 10

Rice ecotypes

●High Yield Potential●Good Grain Quality(High Amylose Content)●Acid-soil Tolerance

Semi‐dwarfindica

Tropicaljaponica

Oryzica Sabana6

Acid soil susceptible (Oryzica 1) and tolerant variety (Oryzica Sabana 6) of upland rice grown on acid savanna soil in Llanos.

Aluminum tolerance of rice and other crops

Aluminum concentration (micro M)

Rel

ativ

e ro

ot le

ngth

(%)

0

50

1000

50

1000

50

100

1 10 100 1000

Wheat(Kinraide 1990)

Maize(Pellet 1993)

Rice

cv. Tyler

cv. South America 3cv. Tuxpeno

Oryzica Sabana 6

Oryzica 1

Species difference in their tolerence to aluminum in the solution culture(in the dilute solution with AlCl 3 and CaCl2 at the pH of 4.0-4.3)

CIAT headquarter at Cali, Colombia

Mechanisms of the adaptation of upland rice genotypes to highly weathered acid soils of savannas in South America

Soil sampling for chemical analysis in savanna field in Llanos Orientales, Colombia

A simple equipment for extracting soil solution by centrifuge

Soil

pH4.24.44.64.85.0 | |

Month

Al i

n so

il so

lutio

n

(m

ic M

)

0

40

80

120

A

B

3 4 5 6 7 8 9 10 11 12 1 2 3

Growth period

Change of pH (A) and Al concentration of soil solution(B) in the surface soil of upland rice field in acid savanna soils.

Al conc. in soil solution (m ic M)0 100 200 300 400

Vertical distribution of soil pH, and Al conc. insoil solution (19 Aug. '93, La Libertad)

pH of soil4.2 4.3 4.4 4.5 4.6 4.7

Dep

th (c

m)

0

20

40

60

80

100

0.3 t/ha lime3 t/ha lime

Days after emergence20 40 60 80 100

Dep

th (c

m)

0

20

40

60

80

100

9

9

9

99

8

8

8

8 8

7

7

7

7 7

98

8

77

7

6

6

6

6

6 66

66

5

5

5 55

4

44 4

3

3 3

20

20

20

40

30

30

987

7

10

10

10

10 1010

10

10

20 40 60 80 100

20

20

99

8 7

4003002009090

8080

7070

6060

5050 50

4040 40

3030 30

20

2020 20

9

9

9

9

9

8

876

8

8

8

7

7

7

6

6

6

5

5

4

10

10

10010010

10

10

10

10

a b

Change by time and depth of the Ca / Al molar ratio of the soil solution of an upland rice field in EasternPlains of Colombia (1994). (a: low lime treatment, b: high lime treatment)

87

(Okada and Fischer 2001)

Exch-Ca (cmol kg-1)

0.2 0.3 0.4Exch-Al (cmol kg-1)

1.5 2.0 2.5 3.0pH

4.4 4.6 4.8Rel

ativ

e yi

eld

(%)

70

80

90

100

110

Al sat. (%)

75 80 85

r=-0.51(ns) r=0.51 (ns)

r=0.58* r=0.43(ns)

Oryzica 1O.Llanos 5

Correlation between relative yield of susceptible varieties of upland rice and several indicators of soil acidity in acid savanna soils.

Conclusions

• The level of soil acidity in savanna soils is not stressful for upland rice.

• Adaptation to low Ca level in soils is the main reason for the better growth of tolerant varieties of upland rice.

• Low requirement of Ca is the main reason for the adaptation of tolerant variety to low Ca conditions.

Roots grown in solutionwith Ca(500uM) and Al(0-600uM)

Cut 0-1 and 1-2 cm tips

Solution (BaCl2, Cit. Acid, EDTA)

Wash solution(Apoplast)---------ICP analysis of Al and Ca

Freeze for 12 hr

Solution (BaCl2, Cit. Acid, EDTA)

Wash solution (Symplast)-------ICP analysis of Al and Ca

Digestion (conc. HNO3)

　(Residual)------------------ICP analysis of Al and Ca

Operationally defined compartmation of Al and Ca in roots(based on Tice et al. 1992 with modification)

Retention of Al and Ca by root surface (cell wall)

Al

0.00.10.20.30.40.50.6

Ca

0.0

0.4

0.8

1.2

u m

ole

Al

g-1 ro

ot fr

esh

wt.

0.0

0.5

1.0

1.5

2.0

u m

ole

Ca

g-1

root

fres

h w

t.

0.0

0.2

0.4

0.6

0.8

Fig. Al and Ca in the apoplastic site of the tip of the roots of Al-tolerant (Oryzica Sabana 6) and Al-susceptible (Oryzica 1) varieties of upland rice grown in different levels of Al in solution culture.

Al in growth solution (uM)0 100 200 300 600

0.0

0.5

1.0

1.5

0 100 200 300 6000.0

0.2

0.4

0.6

0.8

Oryzica 1 (S)O. Sabana 6 (T)

BaC

l 2 e

lute

dC

it. A

cid

elut

edED

TA e

lute

d

(Okada et al. 2003)

ACID SULFATE SOILS94

World Distribution of Acid‐Sulfate Soils (FAO)http://www.fao.org/docrep/005/R5676E/R5676E00.htm#TOC

Acid sulfate soilsFormation 1• Once under the sea, lake or pond, sulfate in the seawater mixed with land sediments containing iron oxides and organic matter. 

PyriteMetal, stable(Brooklincollege)

Iron sulfideAmorphous, unstable(Wikipedia)

• Under such anaerobic conditions, lithotrophicbacteria (eg. Desulforvibrio desulfuricans) form iron hydrogensulfide (H2S), iron sulfide (FeS, unstable), and iron disulfide (FeS2, stable, pyrite). 

Acid sulfate soilsFormation• The pyrites are stable under anaerobic conditions. • From pyrite, jarosite (KFe3(OH)6(SO4)2) is usually formed and accumulated.

Acid sulfate soils

In the lower horizon, jarosite, which is unsoluble to water, is accumulated (circled). 

The pH of the top soil was 4.6 and that of the lower layer was 3.2. 

(Matsunaka 2003)

98Natural Setting - low frequency, low magnitude, short duration acidity

Post Drainage - High frequency, high magnitude, persistantacidity

NSW Primary Industry, Australia

Management of Acid sulfate soilsAerobic conditions create acid soils• Once these soils are drained, hydrogen sulfate will be formed and it becomes extremely acidic.

• 2FeS2 + 9 O2 + 4H2O → 8H+ + 4SO42‐ + 2Fe(OH)3*

*Iron (III) hydroxide (orange) precipitates as a solid.

(The University of New South W l W t

Situation in some countriesIndia  (Samra and Randhawa 1991)• 0.11 million ha mainly in Kerala and West Bengal.• pH 3.2‐3.8 and decreases further with drainage• other limitations are toxicity of Al, H2S and Fe and deficiency of P and Ca

• The best land use of rice cultivation in the standing water

Situation in some countriesMalaysia  (Othman et al. 1991)• Considerable acreage in the coastal plains• limitations are low pH, Al toxicity, nutrient deficiency, susceptibility to flooding and adverse effect of excessive drainage

• once oxidized, pH decreases to 2.6‐3.4 at the depth of 30‐45cm

• Shallow drainage and water table control should be practiced, and the land can be used for oil palm and coconut production. 

CALCAREOUS SOILS

102

Calcareous soils• Soils contain measurable quantities of CaCO3.• Distributing in arid and semi‐arid region.• pH >=7.2     effect of  CaCO3 (pH=8.5) and CO2

• pH=>7.6 is influenced by high salt and/or Na• Adding acid or acid formingmaterials to reduce pHis usually not practical. 

CaCO3 granules on Vertisol

Rainfall and depth of CaCO3

(Havlin et al 2005)

Acidifying materials for calcareous soils• Elemental S

2S + 3O2 + 2H2O <‐> 2SO4‐2 + 4H+

Microbial activity ‐‐ weeks, monthsShould be finely ground and incorporated.

• Sulfuric acid (H2SO4)Quick but needs special equipmentDribbling, knife applicator, irrigation water

• Aluminum sulfate (Al2(SO4)3)For floriculture for azaleas, camellias, etc.Al2(SO4)3 + 6H2O  <‐> 2Al(OH)3 + 6H+ + 3SO4

‐2

• Ammonium polysulfide (NH4Sx)       liquid

Saline, Sodic and Saline‐Sodic soilsOrigin of saline and sodic soils• Arid and semi‐arid regions    <evaporation>rainfall>• Near salt marshes, mangrove swamps, etc. • Irrigation with slightly saline water (eg. Ganges river)

Salts accumulatedNa+, K+, Ca2+, Mg2+, Cl‐, SO4

2‐, HCO3‐, CO3

2‐

Sodium (Na+) is most detrimental for plant andsoil dispersion

Sodium ion increases dispersion and decrease water permeability

DefinitionClassification system for saline, sodic, and saline-sodic soils

(Havlin et al 2005)

saline <pH=8.5< sodicsaline-sodic

Salt tolerance of crops (1)

Salt tolerance of crops (3)

Reclamation of sodic and saline‐sodic soils

Reclamation of calcareous soils