IPADS Soil Fertility Management(2) Soil Acidity, Liming and Alkalinity
Department of Global Agricultural SciencesIPADS
Kensuke OKADA([email protected]‐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