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What are Problem soils?, • Soils which need special management practices for, economic crop production, • Possess characteristics that make them uneconomical, for the cultivation of crops, • Include- Acidic soils and Acid sulphate soils, Salt, affected soils, Waterlogged soils, Organic soils,, soils with physical problems, eroded soils, polluted, soils
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ACIDIC SOILS, • Soil system’s proton (H+ ions) donating capacity, • Got enough of adsorbed exchangeable H+ ions to give, pH <7.0, • Involves intensity and quantity aspects, Intensity- H+ ion activity (pH), Quantity- quantity of alkali required to titrate soil, • More common in humid regions
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Kinds of soil acidity, • Active acidity, Develops due to H+ and Al3+ concentration of the soil solution, • Exchange acidity, Develops due to adsorbed H+ and Al3+ ions on the soil colloids, •, , Residual acidity, Associated with aluminium hydroxy ions and with H and Al atoms, that are bound in non-exchangeable forms by organic matter and, silicate clay, , Total acidity= Active acidity + Exchange acidity + Residual acidity
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Distribution, • Out of 49 million hectares of acidic land, 26 million ha have soil pH <, 5.6 and the rest 23 million ha have pH in range of 5.6 and 6.5, • Acidic soils of India can be classified into seven distinct groups1. Laterite, 2. Laterite and Lateritic red, 3. Mixed red, black and yellow, 4. Ferruginous red, 5. Podsolic brown forest and forest soil 6. Foot hill soil, 7. Peat soils, Soil group, , pH range, , Area, (million ha), , States, , Laterites, , 4.8 to 7.0, , 12.65, , Karnataka, MP, Eastern ghat region, of Odisha , WB, South MH, Malabar, coast, , Laterite and, lateritic red, , 5.0 to 7.0, , 11.80, , Kerala, Odisha, WB, Assam, , Mixed red and 5.5 to 6.5, black/yellow, , 23.66, , Karnataka, Bihar, MP, UP, Jharkhand
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Problems of soil acidity, • Toxic effects, a. Acid toxicity- higher H+ ion conc. toxic to plants, b. Toxicity of different nutrient elements- Fe and Mn, , Browning in rice, , Al toxicity- restrict root growth, restricts absorption and, translocation of P, Ca, Fe and Mn, inhibits microbial activity in soil
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• Nutrient availability, a. Non-specific effects, b. Specific effects, (i) Exchangeable bases- ion uptake and release of bases from, exchangeable form adversely affected. Deficiency of Ca2+ and, Mg2+, (ii) Nutrient imbalances- Availability of P, Mo and B affected, N, K and S become less available if pH <5.5, • Microbial activity, Bacteria and actinomycetes activity reduced (pH below 5.5), Nitrogen fixation affected, Fungi grow well, causing diseases
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Optimum pH for major crops, Crop, , pH range, , Rice, , 5.0-6.5, , Wheat, , 5.5-6.5, , Sorghum, , 5.5-7.0, , Maize, , 5.5-7.0, , Groundnut, , 5.0-6.0, , Mustard, , 6.0-7.0, , Sugarcane, , 6.0-7.0, , Cotton, , 5.0-6.0, , Potato, , 5.0-5.5, , Tea, , 5.0-5.5, , Coffee, , 5.0-6.0, , Banana, , 6.0-7.0, , Mango, , 5.5-6.5
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Amelioration of soil acidity, • Materials that can neutralize the H+ ions of soil solutionAgricultural lime/Liming materials/Agricultural liming, materials, • These are oxides, hydroxides, carbonates and silicates of, calcium or calcium and magnesium, • Calcium oxide, calcium hydroxide, calcium and magnesium, carbonates, slags, H+, , Micelle + CaCO3, , Ca2+ Micelle + H2O + CO2, , H+, , • Gypsum not considered as liming material, CaSO4, Ca2+ + SO42SO42- + H2O, H2SO4
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Factors affecting liming reaction, 1. Moisture- greater the amount of moisture, more, rapid is the rate of reaction, 2. Temperature- Liming materials react more rapidly, at high temperature, 3. Amount of exchange acidity
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Liming materials, • Calcium oxide (CaO)- Unslaked lime/quick lime/burnt, lime/oxide of lime, Manufactured by roasting calcite limestone in a furnace. More, caustic than limestones., CaCO3 + Heat, CaO + CO2, • Calcium hydroxide (Ca (OH)2)- slaked lime/ hydrated, lime/builder’s lime, Produced by adding water to burnt lime. More caustic than, burnt lime., CaO + H2O, Ca(OH)2, • Calcium and calcium-magnesium carbonates- Calcium, carbonate (CaCO3) and dolomite [Ca Mg (CO3)2]. Usually, mined by open pit method.
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• Slags- three types, a. Blast furnace slag- by-product of manufacture of pig iron., Behaves essentially as calcium silicate (CaSiO3), b. Basic slag- by-product of basic open-hearth method of making, steel from pig iron. Impurities in iron (silica and P) are fluxed, with lime and basic slag produced, c. Electric furnace slag- Produced from electric furnace reduction, of phosphate rock during preparation of elemental P. Largely, calcium silicate., • Other liming materials- coral shell, chalk, wood ash, press-mud,, by-product from paper mills, fly ash, sludge, Lime requirement- Amount of liming material required to, raise the pH of the soil to a desired value (6.0 to 7.0)., Depends on soil pH and buffering capacity, Commonly used method in India- Single buffer method, (Shoemaker, McLean and Pratt (1961))
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Efficiency of liming materials, Can be judged on the basis ofa. Neutralizing value (NV) or Calcium Carbonate Equivalent, (CCE) of liming material, Defined as the acid-neutralizing capacity of an agricultural liming, material expressed as weight percentage of calcium carbonate, CCE of liming material= Mol. wt. of CaCO3, x 100, Mol. wt. of liming material, Eg. CCE of dolomite =, Mol. wt. of CaCO3, x 100, Mol. wt. of dolomite, = 100/92 x 100 = 108.7%, Calcium oxide- 179%, Dolomite- 108.7 %, Basic slag- 60-70 %, , Calcium hydroxide-136%, Calcite- 100 %, Blast furnace slag- 75-90 %
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b. Purity of liming material- more purer the liming material,, higher will be its effectiveness, c. Degree of fineness of liming material- fineness increase the, surface area of contact, Measured in terms of ability of a material to pass through a sieve, having 60 holes of equal size in one linear inch (called a 60 mesh, sieve), Efficiency, (%), Material passing through a 60 mesh sieve, , 100, , Material passing through a 20 mesh, but, not a 60 mesh sieve, , 60, , Material passing through a 8 mesh, but, not a 20 mesh sieve, , 20
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Fineness factor- sum of product of the percentage of material in, each of the three size fractions multiplied by the appropriate, effectiveness factor, Effective Calcium Carbonate (ECC) or Neutralizing Index (NI), = CCE x Fineness factor, Liming factor, Defined as the factor by which the actual amount of lime can be, calculated from the estimated theoretical amount of lime. Varies, from 1 to 3.
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Q. Calculate the neutralizing index of the following liming, materialPer cent calcium carbonate equivalent= 90%, 50% material passing through 60 mesh, 25% material passing through 20 mesh, 25% material passing through 8 mesh, Sol. Efficiency rating50% x 100= 50, 25%x 60= 15, 25% x 20= 5, Total efficiency rating/ fineness factor= (50+15+5)= 70, Calcium Carbonate Equivalent= 90%, Therefore, NI of liming material= CCE x fineness factor, = 90% x 70= 90/100 x 70, = 63
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Application of lime, • Application of small amounts of lime in every year or twice, in a year- most effective, • Should be applied well ahead of crop cultivation, • Both surface and sub-surface soils are strongly acidic, (ultisols)- incorporate to a depth of 30 cm (12 inches), • How often must lime be added and how much is needed to, keep the soil pH suitable- Lime Balance Sheet, • Effects of overliming, Deficiency of Fe, Cu, Zn, B, Reduced availability of P and K, Incidence of diseases (like scab in root crops)
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Benefits of liming, •, •, •, •, •, •, •, , Toxicity of Fe and Al reduced, Removal of hydrogen ion toxicity, Increased phosphorus availability, micronutrient (Fe, Mn, Cu, Zn, B) toxicity reduced, Nitrification enhanced- by liming to pH of 5.5 to 6.5, Nitrogen fixation favoured, Soil physical conditions improved- decreases BD,, increases infiltration and percolation of water and checks, erosion, • Control certain plant pathogens- club root disease of cole, crops, • Increases FUE
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Management of AS soils, • Keeping the area flooded, • Controlling water table, • Liming and leaching, May require upto 224 Mt per, hectare within 10 year period
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SALT AFFECTED SOILS, • Soils with excessive concentration of either soluble, salts or exchangeable sodium or both, • pH is 7 or above, with exchangeable complex, dominated by Ca and Mg ions, • Unproductive, occur most extensively in arid climates, • Classified as- saline soil, alkali soil and saline-alkali, soil
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• Salinity expressed in terms of electrical conductivity (EC), measured, in decisiemens per metre (dS/m) (formerly mmhos/cm), • Sodium status usually characterized asa. Exchangeable sodium percentage (ESP)- indicates the degree of, exchangeable complex saturated with sodium., ESP= Exchangeable sodium (C mol/kg) x 100, Cation Exchange Capacity (C mol/kg), b. Sodium Adsorption Ratio (SAR)- indicates comparative concentrations, of Na+, Ca2+ and Mg2+ in soil solution
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Classification, Soil, , EC (dS/m), at 25oC, , pH, , ESP (%), , SAR, , Saline, , >4.0, , <8.5, , <15, , <13, , Alkali, , <4.0, , >8.5 (8.5-10), , >15, , >13, , Salinealkali, , >4.0, , ≤ 8.5, , >15, , >13, , Non salinealkali, , <4.0, , 8.5-10.0, , <15, , <13, , Area under salt affected soils in India- 7 million hectares, Uttar Pradesh- 1.295, Gujarat- 1.214, West Bengal- 0.850, Rajasthan-0.728, Punjab- 0.688, Maharashtra- 0.534
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Saline soil (Solonchalk/White alkali soils), • Contain neutral soluble salts sufficient to interfere seriously with, plant growth (more than 0.1%), (soluble salts- more soluble than gypsum, solubility of 0.241 g per 100 mL of water at 0oC, NaCl- 150 times greater than gypsum), • Cations- sodium (Na+), calcium (Ca2+), magnesium (Mg2+), K+, • Anions- chloride (Cl-), sulphate (SO42-) and bicarbonate (HCO3-), • White crust of salts on the surface
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Sources of soluble salts:, •, •, •, •, •, •, •, , Primary minerals, Arid and semi arid climate, Groundwater, Ocean or sea water, Irrigation water, Salts blown by wind, Excessive use of basic fertilizers, , Process of formation- Salinization
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Criteria to characterize saline soil, • Electrical conductivity (EC) (dS/m), <2- salinity effects are negligible, 2-4- yields of very sensitive crops restricted, 4-8- yields of many crops restricted, 8-16- only tolerant crops yields satisfactorily, >16- only few very tolerant crops yield satisfactorily, • Soluble salt concentration in the soil solution- >0.1 per cent is, injurious to plant growth, • Osmotic pressure (O.P.)- closely related to water uptake, OP (atm or bar)= 0.36 x EC(dS/m), TSS (mg/L)= EC(dS/m) x 640 (if EC<4)
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• Concentration of water soluble boron, Boron concentration (ppm), <0.7 - crops can grow (safe), 0.7-1.5 - marginal, >1.5 - unsafe, • Soil texture
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Sodic/Alkali soils (Black alkali soils/Solonetz), •, •, •, •, •, •, , High concentration of exchangeable sodium, Poor physical condition (deflocculation), Low infiltration and permeability, Toxicity of Na+, HCO3- and OHCharacteristic dark brown or black colour (dispersed humus), Formed by alkalization
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Appraisal of sodic soils, • Exchangeable sodium percentage (ESP), ESP=, Exchangeable sodium (C mol/kg), x 100, Cation Exchange Capacity (C mol/kg), Exchangeable sodium= Total sodium - soluble sodium, • pH, • Sodium Adsorption Ratio (SAR), , Sometimes, regression equation Y= 0.0673 + 0.035 X, used
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Saline-alkali soils, Contains both soluble salts (EC> 4dS/m) and exchangeable, sodium (ESP> 15) (soluble salt content >0.1%), • Properties similar to sodic soils if salts leached down, • Management very difficult, • Formed by combined processes of salinization and alkalization, • Degraded alkali or sodic soils, Extensive leaching of saline-sodic soil , causing replacement, of exchangeable Na by hydrogen, Clay Na + H O, H Clay + NaOH, 2, NaOH + CO2, Na2CO3 + H2O, Sub surface horizon, , Process of breakdown of H-clay under alkaline conditionsolodisation
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Calcareous soils, • Contain sufficient amount of lime (CaCO3) and often, magnesium carbonate (MgCO3) throughout the profile, • Show alkaline pH on hydrolysis of lime, CaCO3 + 2H2O, Ca(OH)2 + HCO3- + H+, Ca(OH)2, Ca2+ + 2OHCarbonates interfere with the solubility of phosphate and iron
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Problems of salt affected soils, • SALINE SOILS, 1. Effects absorption of water and nutrients, 2. Salt toxicity- root injury, inhibition of seed germination, , •, 1., 2., 3., 4., 5., , SODIC SOILS, Dispersion of soil colloids, Other physical properties affected- aeration, HC, drainage, Caustic influence, High concentration of hydroxyl ion, Specific ion effect- deficiencies of Ca and Mg
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RECLAMATION OF SALF AFFECTED SOILS, 1. Leaching, Very effective method for ameliorating saline soils, Leaching requirement (LR)- Defined as the fraction of irrigation, water that must be leached through the root zone to control soil, salinity at any specified level. Expressed as fraction or per cent., LR = Depth of drainage water or, EC of applied water, Depth of irrigation water, EC of drainage water, Q. Calculate the leaching requirement if irrigation water is, having EC of 3dS/m and that of drainage water is 8 dS/m., Sol. LR= Eciw x 100 = 3 x 100= 37.5 %, Ecdw, 8
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2. Use of chemical amendments, For converting part of caustic alkali carbonates into sulphates,, which are ultimately lost by leaching., Different amendments are suitable for different soil conditions., Soil conditions, , Amendments, , Saline and alkali soils having pH range, upto 9.0, , Gypsum, , Alkaline and saline-alkali soils having, pH range 8.0-9.0, , Sulphur, Iron sulphate, Iron, pyrite, , Saline soils having pH less than 8.0, , Limestone
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Gypsum (CaSO4.2H2O), Loss of exchangeable sodium occurs and calcium take place of, sodium on exchange complex., Na2CO3 + CaSO4, CaCO3 + Na2SO4, Clay, , Na, , + CaSO4, , Ca, , Clay, , + Na2SO4, , Na, , Considered best and cheapest for reclamation process, Gypsum requirement (GR)- The amount of gypsum required to, lower the ESP of a sodic soil to a desired level (10 and below), GR (Ca2+ per 100g of soil) = [ESP (initial) – ESP (final)] x CEC, 100, GR= (C1-C2) x 2meq of Ca2+ per 100g of soil, GR (t/ha) = GR (Ca2+ per 100g of soil) x 1.72, Gypsum factor=1.25
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3. Salt precipitation, Salts can be leached out to only 0.9-1.8 m (3-6 ft) depth, instead of, leaching salts completely away, 30% of total salts may eventually precipitate, 4. Choice of crops, Highly salt resistant crops- Barley, sugarbeet, cotton, safflower, taramira, Rape, Moderately salt resistant crops- wheat, rice, maize, pearl millet, oats,, sunflower, potato, pomegranate, Low salt resistant crops- beans, radish, carrot, onion, apple, grapes, citrus, Tolerant to sodicity- Rice, sugarbeet, sugarcane, cotton, paragrass, millet, Semi-tolerant to sodicity– Wheat, barley, oats, maize, gram, peas, Sensitive to sodicity- Groundnut, cowpea, lentil
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WATERLOGGED SOILS / SUBMERGED SOILS, , •, , •, •, •, , Soils that are saturated with water for sufficiently long time, Major problemsoxygen shortage, (root growth ceases when ODR< 20 x 10-8 g/cm2/min), production and accumulation of harmful compounds, decreased nutrient availability (Zn, Cu, Mg, Ca, S),, N losses, Redox potential (Eh) of waterlogged soils: -250 to -300 millivolts, (well aerated soils: 400-700 millivolts), Area under waterlogging in India- 8.5 Million ha, (West Bengal- 2.18 M ha, UP- 1.98 M ha)
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Management, •, •, •, •, •, •, , Improving land drainage, Leveling of field, Adjusting planting dates, Cover crops, Planting on raised beds, Raising tolerant crops, Highly tolerant, , Medium tolerant, , Sensitive, , Rice, jute, daincha, Wheat, barley, oats, Maize, tobacco,, sugarcane, coconut, sorghum, cotton,, most legumes, date palm, banana
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Organic/ Peat soil, Soil consisting largely of undecomposed or slightly decomposed, organic matter accumulated under conditions of excessive, moisture, Organic soils (histosols) with >20% organic matter content, (plants can be differentiated), Heavy and black in colour, Found in Kerala, Odisha, West Bengal (Sunderbans), SE coast of, Tamil Nadu
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Soils with physical problems, 1. Slow permeable soils, Very high clay content, infiltration rate < 6cm/day, so more runoff, which eventually leads to soil erosion and nutrient removal, poor, aeration, reduced conditions, 2. Soil surface crusting, Due to the presence of colloidal oxides of iron and aluminium in, soils which binds the soil particles under wet regimes. On drying, it forms a hard mass on the surface. Predominant in Alfisols., 3. Sub soil hard pan, Commonly found in red soils. Though soil is fertile, crops cannot, absorb nutrients from the soil which leads to reduction in crop, yields
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4. Shallow soils, Shallow soils are formed due to the presence of parent rocks, immediately below the soil surface ( 15-20 cm depth)., 5. Highly permeable soil, Sandy soils containing more than 70 per cent sand fractions occur, in coastal areas, river delta and in the desert belts., 6. Heavy clay soils, Heavy have very hard consistence when dry and very plastic and, sticky ("heavy") when wet. Most of the heavy clay soils belong, Vertisols, 7. Fluffy paddy soils, Puddling results in substantial break down of soil aggregates into, a uniform structure less mass.
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