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Topic: Problem soils, , 1
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Problem soils, • Soils that have serious constraints for crop, production and that needs special management, techniques are called as problem soils., • They can be defined as the soils which possess, characteristics that make them uneconomical, for the cultivation of crops without adopting, proper reclamation measures
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Problem soil Vs Degraded soils, • Degraded soils which, unwise management, create supplementary, productive problems., • The limitations may be, biological, , are produced by interventions which, environmental and, physical, chemical or
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Classes of problem soils, I, , •, •, •, •, •, •, •, •, •, •, •, , Cold soils, Dry soils, Steep soils, Shallow soils, Poorly drained soils, Coarse textured soils (Sandy soils), Heavy cracking soils (Vertisols), Poorly fertile soils, Salt affected soils –saline, sodic, saline-sodic, Acid sulphate soils, Peat soils (organic soils).
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II, •, •, •, •, •, , Soils that faces climatic problems, Soils with physical problems, Soils with chemical Problems, Soils with biological Problems, Soils with nutritional problems due to above, constraints, • Soils that faces problems due to anthropogenic, reasons
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Classification of problem soils based on the nature of problems, Nature of problem, Climate, Physical, , Chemical, , Biological, , Cold soils, , Steep soils, , Acid soils, , Dry soils, , Shallow soils, , Acid sulphate Soils with low Soils, soils, biological, nutrient, activity, toxicity, Saline soils, , Imperfectly, drained, /, submerged soils, Surface, crusted Saline, soils, soils, , sodic, , Soils with hard Sodic soils, pan, Highly permeable, soils, Heavy clay soils, Organic soils, , Low, soils, , Nutritional, , carbon Nutrient, deficient soils, , Anthropogenic, Mine soils, , with Eroded soils, , Man, made, polluted soils, Degraded soils
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I. SOILS WITH CLIMATIC PROBLEMS, , a. Cold soils (Frozen soils), • These soils are generally found in temperate and high altitudes areas, • Mean temperature for a day will be < 5o C during the growing period., , • Skeletal soil and calcareous in nature., • Natural vegetation comprises sparse forests., • Cultivation is very much limited., • Temperate fruit trees like apple, apricot and cool season vegetables, are cultivated.
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Management, • Adjust planting time, • Choose cold tolerant plants, , • Mulching, • Choose protected cultivation, , • Follow scientific crop management practices
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b. Dry soils, • Found in desert and semi-desert areas where the water deficit, prevails throughout the year, , • The natural vegetation is mainly sparse sporadic thorn forest., • Extreme dryness will result cracking of soils and destroys soil, structure, , • The annual rainfall is low (<400 mm) and potential, evapotranspiration is very high (1500mm), • Length of growing period <90 days, • Salt accumulation, • These soils are deficient in N, P, Zn and Fe but are rich in bases, like Ca and Mg.
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Management, •, •, •, •, , Provision of mulches,, Addition of organic manure, Adaption of scientific irrigation practices, Follow conservation tillage for better moisture retention and, water use by crops, • Judicious use of soil amendments and fertilizers, • Plant drought tolerant crops
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II. SOILS WITH PHYSICAL PROBLEMS, , a) Steep soils, • Percentage slope is >30, • The annual rain fall is >2000 mm., • These soils rarely experiences water stress, but the, soils are very shallow, • Steep slopes, • Soil erosion, • Poor soil fertility, • Shallow depth, • Decline in soil fertility and increase in soil acidity
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Management, • Appropriate engineering/agronomic soil, conservation methods, • Protect the soil with geotextiles / crop covers/, or other artificial structures, • Use soil binding agents to improve soil, structure
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b)Shallow soils, • Found on hill tops and along the slopes., • Characterized by the presence of shallow, cemented horizons., • Presence of parent rocks immediately below, the soil surface (15-20 cm depth) results in the, formation of shallow soils., • Experience frequent droughts due to lack of, sufficient soil depth
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• Low water holding capacity, • Soil depth is the main limitation, • Presence of hard pan or rock or any salt, deposits within 50 cm from soil surface, • Root penetration will be restricted resulting, poor crop growth, • Due to shallowness, less volume of soil is, available for roots to proliferate and hence, very low nutrient availability
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Management, • Growing shallow rooted crops or crops that can, withstand shallowness, • judicious use of organic manures and fertilizers, • scientific and careful irrigation methods, • Adopt slope protection measures on hill sides, • Raising of grass or crops with strong anchorage, • Cultivate erosion resistant crops, • Deep ploughing, breaking of hard pans, application, of organic manures
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c)Poorly or imperfectly drained or slowly, permeable soils/submerged soils:, • Poor drainage due to high clay content or presence of shallow, water tables., • Soils which are waterlogged or remains under water for major, period, • Reasons, – high clay content;, – shallow water table;, – presence of hard pans;, – poor physical conditions resulting from sodicity;, – landscape position;, – compaction;, – blockage of soil pores with minute colloidal particles
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•, •, •, •, •, •, •, , Waterlogging, Problems with salinity /acidity, Elemental toxicities, Loss of nutrients in water, Low organic matter decomposition, Low microbial activity, Deficiency of nitrogen, sulphur, zinc and boron
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Management, Nutritional management, •, •, •, •, , Application of organic manures, Application of lime to correct pH / soil acidity, Use of controlled release fertilizers for N, Adopt method for increasing nutrient use efficiency (slow, release / coated fertilizers, nitrification inhibitors, urease, inhibitors, deep placement of urea balls etc), • Use of rock phosphate, • Promote use of bio fertilizers, • Scientific management of water and nutrients
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General management, • Select Suitable crops that can tolerate waterlogged condition, • Select suitable planting methods like - planting on ridges or, mounds, • Addition of soil amendments/ conditioners, • Incorporation of organics, • Provision of drainage, • Deep ploughing, , • Formation of ridges and furrows, • Formation of broad beds
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d) Surface crusted soil, • Soil crusts are specific modifications in the top soil caused by, natural events such as raindrop impact and the following drying, process, • Their thickness usually ranges from less than 1 mm to 5 cm., • The soils having weakly aggregated soil structure are easily, broken by the impact of rain drops resulting in the formation of, clay crust at the soil surface., • 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., • Clay soils, especially those with high magnesium content and/or, sodium content, are prone to soil crusting
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Mechanism of crust formation, • Mechanical destruction of soil surface aggregates, by raindrop impact, • Leaching of fine particles and their subsequent, deposition in the underlying pores, • Compaction of soil surface to form a thin film, which restrict both the further entry of water and, the movement of fine particles in the soil pores, • Cementation of the slaked soil at the soil surface, due to the drying and reorientation
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• Structural crusts- formed by above mechanism, • The crusts can also be formed by translocation, of fine soil particles, deriving from the, destruction of surface soil aggregates, and their, deposition at a certain distance from their, original location- “depositional crusts”, • To study soil crusting, pocket penetrometer is, be used., • It provides accurate measurements of the, compressive soil strength and is expressed in, kg/sq. cm or dynes/sq.cm.
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Impact of crusting on soil properties, , • Prevent germination of seeds and retards root growth, • Results in poor infiltration and accelerates surface, runoff, • Creates poor aeration in the rhizosphere, • Affects nodule formation in leguminous crops
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Management, • Ploughing is to be done when the soil is at optimum moisture, regime., • Lime or gypsum @ 2 t ha-1 may be uniformly spread and another, ploughing is to be given for blending of amendment with the surface, soil., • Farm yard manure or composted coir pith @ 12.5 t ha-1 or other, organics may be applied to improve the physical properties of the, soils, • Scraping the surface soil by tooth harrow will be useful., • Bold grained seeds may be used for sowing on the crusted soils., • More number of seeds/hill may be adopted for small seeded crops., • Sprinkling water at periodical intervals may be done wherever, possible., • Resistant crops like cowpea can be grown.
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e) Soil with sub soil hard pan, • Hardpan is a dense layer of soil, usually found below, the uppermost topsoil layer, • They are largely impervious to water, • formed by deposits in the soil that fuse and bind the, soil particles- dissolved silica iron oxide and Calcite, • Man made- hardpan formed by compaction from, repeated ploughing, particularly with moldboard, plows, or by heavy traffic or pollution, • Having high bulk density(>1.8 Mg m-3), • Impeded drainage and restrict the root growth
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Management, • The hardpan can be broken up by either, mechanical means such as digging or ploughing,, or through the use of soil amendments, • Addition of soil organic matter through manure,, compost or peat, , • Improve, , local, , drainage, , proliferation of earth worms, , and, , promote, , the
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f) Highly permeable soils, • sandy soils containing > 70 % sand and clay, content < 18%, – Somewhat excessively drained-Water is removed, from the soil rapidly, – Excessively drained: Water is removed very, rapidly
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• Very high infiltration rate and hydraulic conductivity, • Low moisture retention and water holding capacity, , • Generally poor in organic matter and nutrients,, • Low in bases like Ca, Mg and K, • Low in micronutrients viz., Zn, Cu and B, , • Poor structure or weak aggregation, hence applied nutrients are, easily lost from soil, • Less anchorage to the crops grown, , • In extreme hot areas, root growth is limited due to high soil, temperature
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Management, • Uniform ploughing, • Application of clay soil up to a level 100 t ha-1 based on the, severity of the problem, • Application of organic materials like farm yard manure,, compost, press mud, sugar factory slurry, composted coir pith,, sewage sludge etc. to improve soil structue, • Providing asphalt sheet / polythene sheet below the soil, surface to reduce the infiltration, • Crop rotation with green manure crops like sunhemp, sesbania,, daincha, Frequent irrigation with low quantity of water, • Provide mulching, • Frequent split application of fertilizers and use of slow release, fertilizers like neem coated urea.
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g) Heavy clay soils / Heavy cracking soils, (Vertisols), • Slowly permeable soils., • Heavy clays have very high water-holding capacity, but most of, the water is tightly bound and not available to plants, • Black or dark coloured soils rich in montmorillonite clay (>30%), • They swell on absorption of water and shrink on drying. During, this process, soils develop cracks of about 1 cm wide. The cracks, are wedge shaped and on drying, soil will fall into these cracks, resulting inversion of soil. Hence there is no horizonation, • Consists of mainly poorly drained clayey soils, • High in CEC and base saturation
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• Calcium carbonate nodules are present, • Under poor drainage, leaching of weathering products are, restricted and hence a pH > 7 are shown by these soils. They, are rich Ca and Mg, • The fertility status is high, but unbalanced. N and P are, generally low and high in Ca and Mg, • If sustainably managed these soils can ensure crop production, without much cost, • Faulty irrigation results the development of saline or sodic, soils, • Deficient in micronutrients
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Gilgai, – The process of opening and closing of cracks produce, a characteristic relief, known as gilgai., Slickensides, -The contraction of the aggregates during the dry, season results the formation of deep wedge shaped cracks, (spenoids) in vertisols., – In the rainy season, the water enters the wedges and, the aggregates expands (swells) closing cracks., – Continuous expansion/contraction leads to a uniform, distribution of clay particles in the surface of, aggregates., – These pressurised reflective surfaces are known as, slickensides a characteristic phenomenon of Vertisols.
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• Very difficult to maintain optimum moisture, • Slight variation on lower/higher side causes poor, physical condition, • Heavy /mechanical tillage results compaction, • Ploughing should be done at optimum moisture, • Swelling & drying problems, • Low in N, P, Fe, Mn and Zn
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Management, •, , Follow scientific tillage and water management, , •, , Improve surface drainage in poorly drained soils by adding materials like sawdust or coirpith, and /or provision of subsurface drainage / addition of soil amendments, , •, , Adopt water harvesting techniques in dry areas, , •, , Application coir pith / organic manure / green manure improves physical condition of soil, , •, , Follow scientific irrigation and nutrient application. Fertigation is an ideal option to these, soils, , •, , Select suitable cropping systems, , •, , Make raised beds
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h)Fluffy paddy soil, • They are characterized by low bulk density of top soil, resulting sinking of farm animals and labourers as well, as poor anchorage to rice seedlings., • The soil particles are always in a state of flux and the, mechanical strength is lost leading to the fluffiness of, soils., • In Kerala, fluffy paddy soils are prevalent in Chittoor, district of Palakkad (Poonthal padam soils)., • It is formed due to the continuous rice-rice cropping, sequence.
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Impact of fluffiness, , • Sinking of draught animals and labourers, • Low bulk density and very rapid hydraulic, conductivity
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Management, • The irrigation should be stopped 10 days before the, harvest of rice crop., • After the harvest of rice, when the soil is under semidry condition, compact the field by passing 400 kg, stone roller or tar drum filled with 400 kg of sand for, 8 times., • The usual preparatory cultivation is carried out after, compaction.
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III. SOILS WITH CHEMICAL PROBLEMS, , a) Acid soils, • Acid soils are characterized by the preponderance of, H+ ions, • H+ found in soil solution, Fe3+ and Al3+ found in soil, matrix or in solution are largely responsible for soil, acidity
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Sources of soil acidity, • Leaching due to high rainfall- In high rain fall areas,, most of the bases like Ca, Mg, K, Na etc. will be, leached out, resulting an accumulation of Fe and Al in, soil which are acidic in nature, • Parent materials, • Humus and organic matter: The acidity is due to the, H+ ions of carboxylic and phenol groups, • Aluminosilicate clays- The H+ ions due to permanent, charges and pH dependent charges
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• When the pH is below 4.5, H+ ions replace some of, Al3+ ions and release to the soil solution. The Al3+, undergoes subsequent hydrolysis, – Al3+ + H2O → Al(OH) + H+, – Al(OH) + H2O → Al(OH)2 + H+, – Al(OH)2 + H2O → Al(OH)3 + H+, Gibbsite get precipitated in acid range, – Al(OH)3 + H2O → Al(OH)4 + H+ (Occurs in, alkaline range)
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• Oxides, hydrous oxides and polymers of Fe and Al:, Undergo stepwise hydrolysis and release H+ ions, • Production of CO2, , • Nature of soil colloids: When H+ ion is the dominant, cation of soil colloids, the soil become acidic and if, basic cations like Ca, Mg or Na are dominant the soil, will be basic in reaction., • Low Percentage Base Saturation (PBS) and kinds of, bases, • Soil management: Addition of acid forming fertilisers, results soil acidity, • Oxidation reduction potential- On submergence- Self, liming occurs
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Classification of soil acidity, Based on source of H+ ion, • Active acidity, • Exchangeable or salt replaceable acidity, • Potential acidity
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Active acidity, • It is a measure of H+ ion activity in soil solution., • The Al3+ present in the soil solution undergoes, hydrolysis and contributes to active acidity, • Very small compared to others- directly affect plants, • By measuring pH of a soil suspension, active acidity, , is measured.
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Exchangeable acidity, •, , It is mainly associated with exchangeable H+ and Al3+, , adsorbed on soil colloids, • These ions can be released to soil by unbuffered salt solution, such as KCL., , • Exchangeable acidity is represented by H+ and Al3+ that are, easily exchangeable by other cations in a simple unbuffered, salt solution., , • It is the acidity extracted by 1 M KCl solution and determined, by titrating the extract with standard alkali.
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Potential acidity:, • Also known as extractable acidity or reserve acidity or residual, acidity or even titratable acidity, • Mainly associated with non exchangeable H+ and Al3+ that are, bound in non exchangeable sites by organic colloids and silicate, clays., • Remains in soil after the neutralization of active and exchange, acidity., • Indicates the acidity that can be neutralized by liming materials, but, cannot be detected by salt replaceable techniques., • Several times greater that active and exchangeable acidity., • Represents the acidity extracted by BaCl2-TEA buffer solution at pH, 8., , • Total acidity, =Active acidity + Exchange acidity (+ Residual acidity)
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CLASSIFICATION OF ACID SOILS, A. Based on soil pH, Class, , SOIL TYPE, , pH range, , 1, , Slightly acidic, , 6-6.5, , 2, , Moderately acidic, , 5.5-6, , 3, , Strongly acidic, , 5-5.5, , 4, , V. Strongly acidic, , 4.5-5, , 5, , Extremely acidic, , 3.5-4.5, , 6, , Ultra acid, , <3.5
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B. Based on Organic Matter Content, 1. Acid Mineral Soils, - Organic matter < 20%, - Includes, a. Podzols, b. Laterites, 2. Acid organic soils, • > 20% organic matter (12% OC) if clay is low and minimum, 30% om upto 50% clay, • Formed – heavy vegetation + high rainfall and water logging, Peat soils, - Large amount of o.m. not fully decomposed, Muck soils, - Organic matter highly decomposed
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PROBLEMS OF SOIL ACIDITY, A. Direct effects, 1. Toxic effect of H+ on root tissues., 2. Soil Enzymes -lose effectiveness, 3. Mineralization - slow, 4. Disturbance in acid- base balance in plants
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PROBLEMS OF SOIL ACIDITY, B. Indirect effects, 1. Toxicity of Different Nutrient Elements, , a. Iron and Manganese., A physiological disease of rice in submerged soils – browning,, bronzing, wilting, b. Toxicity of Aluminium (Al), Al retard root growth and cell multiplication
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PROBLEMS OF SOIL ACIDITY……, 2. Nutrient imbalances, , - Soluble iron, aluminium and manganese toxic in highly acid, soils., - Phosphorous - unavailable - Fixation of P by hydrous oxides, of Fe and Al or by adsorption, - Fe, Mn, Cu and Zn abundant, Mo - very limited, - Very low pH - availability of B decreased due to adsorption, on sesquioxides, Fe and Al hydroxyl compounds, -N, P and S - less available if pH less than 5.5.
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PROBLEMS OF SOIL ACIDITY……, 3. Microbial Activity, - pH < 5.5 - activity of bacteria, actinomycetes reduced, - Nitrogen fixation affected by inhibiting Azotobacter sp., - Inhibits symbiotic nitrogen fixation by affecting rhizobium sp., , - Fungi - diseases like root rot of tobacco, blights of potato etc.
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Management, ▪ By land use, depending on aluminium concentration, In high Al soils: shifting cultivation in forest systems using, slash-and burn practices, (short term tuber and root crop), In low Al soils: Regular liming., ▪ Use of charcoal and biochar, ▪ Burning vegetation, provides ashes like CaO and MgO neutralize Al, ▪ Use of Organic Waste Materials and wood ash- wood ash, compost, ▪ Lowlands – flooding - raise pH of the soil., ▪ Use of basic fertilizers, ▪ Acid tolerant crops like rice, potato, tea , wheat, sweet potato,, maize, brinjal, pepper etc. to be cultivated
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Liming Materials, • Materials that are necessary for the neutralization of soil, , solution hydrogen (H+) ions., • ie., , Oxides,, , hydroxides, carbonates and silicates, , of calcium and magnesium., • ie. the accompanying anion must be one that will reduce, the activity of hydrogen (H+) ions and hence aluminium, in soil solution., • These are called “Agricultural liming materials”.
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Factors affecting liming reactions, • Moisture : Greater the moisture content, more rapid, the rate of liming reactions., , • Temperature : The preferred temp range is between, 20 and 25 oC, • Exchange acidity : Greater the exchange acidity, more, rapid the liming reactions
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• Agricultural Liming material- A material whose Ca and Mg, compounds are capable of neutralising soil acidity, eg., • Quick lime (CaO)-Manufactured by roasting calcite by the, removal of CO2, • Calcite - Obtained from shells or ground lime stone, • Dolomite CaMg(CO3)2, • Hydrated lime Ca(OH)2, • Ca, Mg silicates, • Marl-Mainly CaCO3 and present in lake bottoms, • Slag:, – Blast furnace slag: By product of pig iron industry, – Basic slag: By product of basic Open Hearth process for steel, production, – Electric furnace slag: Produced during the electric furnace, reduction of phosphate rock for the manufacture of elemental P
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Efficiency of liming materials, • The efficiency of liming materials is evaluated on the, basis of, – Neutralising value or calcium carbonate equivalent, of liming materials, – Purity of liming materials, – Fineness of liming materials
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1. Neutralising value (N.V), , • Calcium carbonate equivalent (CCE): It is the acid, neutralising capacity of agricultural liming materials, expressed as a weight percentage of calcium, carbonate, • CCE, , Molecular weight of calcium carbonate x 100, = ---------------------------------------------------Molecular weight of liming material
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Neutralising value, Liming material, , Neutralizing value, , Calcite, , 100, , Quick lime, , 179, , Dolomite, , 109, , Slaked lime, , 136, , Calcium silicate, , 86, , Magnesium carbonate, , 84
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2.Purity: Presence of contaminants reduces the effectiveness, of liming material., , 3. Fineness of liming material: More fine the material, more, effective., • For evaluating fineness a “Fineness factor” is derived, , based on size of liming material, • Neutralizing index is calculated by multiplying CCE with, fineness factor., – Neutralizing index (NI)= CCE x Fineness factor, Per cent Effective Calcium Carbonate or NI
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Lime requirement, Lime requirement is defined as the quantity of liming, materials to be applied to soil for increasing soil pH to a, desired value, usually 6.5., Fcators, • Required change in pH, • Buffering capacity of the soil, • Chemical composition of liming material and, • Fineness of the liming material, • Depth or amount of soil to ameliorate, Lime requirement- SMP buffer method and Exchangeable, Aluminium Method, SMP- proposed by Shoemaker, Mc Lean and Pratt
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BENEFITS OF LIMING, • Increases the N availability by providing a favourable, environment for organic matter decomposition by, microbial action, • Increases P availability in acid soils, • make K utilization more efficient, by preventing excess, uptake of K, • Supply Ca and Mg, • Make Mo available, • Reduce the availability of Fe, Mn and Al and prevent, their toxicity, • Enhances root development and improves soil, structure.
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Effects of over liming, • Deficiency of Fe, Mn and Zn, • Reduced availability of P and K, , • Boron deficiency may occur, • Root development may be hindered due to the, dominance of OH- ions, • Incidence of Scab disease in root crops.
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b) Acid sulphate soils (Cat clays), Acid sulfate soils are the soils that have elevated, concentrations of metal sulphides which generate acidic, conditions on exposure to air., Characteristics, • Presence of sulfuric horizon or sulphidic materials with a pH, <4., • Accumulation of pyrites, • Chemical limitations: Extreme acidity ,iron, aluminium and, sulphur toxicities, • Root development is restricted; water reserves in sub soil are, not available, • Presence of yellow mottles of jarosite in oxidized condition, • Akiochi disease
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Classification of acid sulphate soils, • True acid sulphate soil, – Possesses a highly acidic soil layer containing sulfuric, materials produced by the oxidation of sulfidic, materials present, – pH <3.5 and can usually be identified by the presence, of bright yellow jarosite mottles or streaks., , • Potential acid sulphate soil, – Has the potential to develop actual acid sulphate, condition when exposed to air or drained., – It is composed mostly of accumulations of iron sulfide, minerals
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The pre-requisites for the formation of acid, sulphate soils are, • Source for sulphur, • Presence of excess quantities of iron, • Supply of organic matter, • Anaerobic or flooded condition
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Genesis of acid sulphate soils, , It includes, – Cumulative and reductive geochemical phase and, – Oxidative phase followed by, – Neutralization phase
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b) Oxidation of Pyrite, • The fine-grained pyrite is readily oxidized upon exposure to, air, giving Fe (II) sulfate and sulfuric acid:, • The rate of oxidation is enhanced by Thiobacillus ferroxidans, which is active under pH below 3.0., 2FeS2 + 7O2 + 2H2O → 2Fe2+ + 4SO4 2- + 4 H+, • Pyrite is oxidized more rapidly by dissolved Fe (III) than by, oxygen, according to the following reaction, FeS2 + 14Fe 3+ + 8H2O → 15Fe 2+ + 16 H+ + 2SO42-
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c) Neutralization phase, • The sulphuric acid formed reacts with bases in, sediments, • The most prominent compounds are jarosite, oxides, of iron and gypsum., • Sediment containing pyrite becomes a potential acid, sulphate soil only when the potential acidity exceeds, the neutralization capacity of the soil, ➢ Jarosite (KFe3(SO4)2(OH)6) - formed only in, extremely acidic (pH 2 to 4) and oxidized (Eh > 400, mv) environments., – The pale yellow color, Metastable, eventually be, hydrolyzed to goethite
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➢Iron Oxides, Most of the iron from oxidized pyrite ends up as Fe, (III) oxides, Fine-grained goethite formed, – Fe 2+ + SO4 2- + 1/4 O2 + 3/2 H 2O → FeOOH +, 2H+ + SO42– Jarosite → 3FeOOH + 2S04 2+ + K+ + 3H+, • In the better drained, deeply developed acid sulfate, soils, part of the Fe (III) oxides in the B horizon may, occur as hematite, giving conspicuous red mottles.
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➢ Gypsum, – If soils contain an appreciable amount of a neutralizing, compound such as CaCO3, the precipitation reaction, could occur:, – 2CaCO3 + KFe3(SO4)2(OH)6, , + 5H2O + H+ →, , 2CaSO4. 2H2O + 3Fe (OH)3 + K+ + 2CO2, – The formation of gypsum in acid sulfate soils is an, indication of the soils being relatively suitable for, agriculture.
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Fate of acidity, • The acidity produced can be neutralized by CaCO3 present in, the soil or by added limestone, finally producing gypsum., , – CaCO3 + 2H+ + 2SO4 + + H2O → CaSO4. 2H2O + CO2, • During flooding acidity is alleviated due to the consumption of, H+, • At pH values below 3.5, Al toxicity is the principal hazard,, though Fe and H are present in toxic quantities., • H2S toxicity is also prevalent as a result of sulphate reduction,, but the presence of Fe2+, reduce its intensity by forming iron, sulphides.
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Nutrient deficiencies, • mainly deficient in phosphates and bases like, Ca, Mg, K, Zn, Cu, • The presence excess quantities of Al, Fe and H
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Management, • Keep the soils in flooded condition as long as, possible, • Drainage : Provision of shallow surface or subsurface, drainage, • Application of amendments: Liming materials to, neutralize soil acidity, • Practice alternate rice and shrimp cropping, • Application FYM / indigenous amendments
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c) Salt Affected, , Soils, , • Salt affected soils are that soils contain considerable, amount of soluble salts and/or sodium on exchange, complex., • They occur in areas where potential evapotranspiration, exceed the precipitation ie., in arid and semi arid regions, • The soluble salts generally present are the chlorides,, sulphates, cabonates and bicarbonates of sodium,, magnesium and calcium, • In India, salt affected soils occur in an area of about, 6.745 million ha
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Reasons for salt build up or salinity, Genetic reasons., – Parent material, – Arid climate, – Sea water intrusion, , Anthropogenic reasons, – Irrigation with poor quality water, – Seepage from canals, – Deposition of salts on soil surface from high subsoil, water table, – Faulty land use
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Chemical characterization of salt affected soils, , Exchangeable sodium percentage (ESP):, • It is the percentage of exchangeable Na ions, to CEC of the soil, • ESP =, , Exchangeable Na (cmo/kg) x 100, ------------------------------------------Cation exchange capacity (cmo/kg), , • Safer limit of ESP is <15.
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Sodium absorption ratio (SAR):, • This is used to estimate the amount of sodium, in relation to other cations., • It gives information on comparative, concentration Na+, to Ca 2+ and Mg 2+., • SAR, =, Na (meq/lit), Ca2+ + Mg2+ (meq/lit), 2, , 1/2
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Electrical conductivity of the saturation extract or, Salinity:, Salt concentration is estimated on the basis of the ability of, the salt in soil solution to conduct electricity., The electrical conductivity is directly proportional to the total, soluble salt concentration., Laboratory measurements of EC of the saturation extract of, soil in practiced., It is expressed in dS/m., , pH (1:2soil : water suspension or saturation extract)
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Classification of salt affected soils, Saline soils:, • contain a concentration of neutral soluble salts, sufficient to interfere seriously with the growth of, most plants., • The EC of saturation extract is greater than 4, dS/m, ESP<15, SAR < 13 and pH less than 8.5,, • The chlorides and sulphates of the base forming, cations are dominating., • Saline soils are called white alkali/ solonchaks, because of the surface encrustation of salts present in, white colour.
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Saline-sodic soils or saline-alkali soils:, • These soils contain appreciable quantities of neutral, , soluble salts and enough Na ions to seriously affect the, plant growth., • ESP>15, EC of saturation extract > 4 dS/m and pH, ≤ 8.5 because of the presence of neutral salts,, SAR>13, , • Upon leaching, when free salt content decreases, these, soil may behave like a sodic soil
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Sodic soils or Alkali soils:, • Sodic soils contain very small quantities of soluble, salts but are rich in Na salts, • The high pH is largely due to hydrolysis of sodium, carbonate, alkaline hydrolysis, • The Na on exchange complex also undergoes, hydrolysis., • The EC of saturation extract is less than 4 dS/m,, ESP>15, SAR >13 and pH is more than 8.5,
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• Due to the deflocculating influence of Na, sodic soils, have very poor physical characteristics, , • soils is usually discoloured by the dispersed humus, carried upward by capillary water and deposited at, the surface when it evaporates. Hence these soils are, called as Black alkali., • Sodic soils- Black alkali soils- Solonetz, • Slick spots- If the sodic soil occur in small areas are, often called as Slick spots
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Comparison of properties of salt, affected soils, Property, , Saline soil, , Saline-sodic, , Sodic soil, , soil, < 8.5, , ≤ 8.5, , >8.5, , >4, , >4, , <4, , SAR, , <13, , At least 13, , >13, , ESP, , <15, , >15, , >15, , pH, EC of saturation, extract (dS/m)
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Effects of high salt concentration, •, •, •, •, •, , Inhibit or slows down seed germination, Adversely affect the growth of plants, Toxicity of bicarbonate and other anions, Low nutrient availability under high pH, Breakdown of structure which cause oxygen oxygen, depletion, poor infiltration and percolation, • High chloride content in association with Na – causes, leaf damage
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Classification of crops based on salt tolerance, Tolerant Plant, , Moderately tolerant Moderately sensitive, , Sensitive, , Sugar beet, , Wheat, , Rice, , Lemon, , Date, , Sorghum, , Pea, , Onion, , Cotton, , millets, , Cabbage, , Tomato
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Salt balance (Scofield ,1940), • The relationship between the quantity of salt brought, into an area with irrigation water and the quantity of, salt removed in the drainage water, , Leaching requirement, • Additional water needed for leaching, over that, needed to wet the profile is called leaching, requirement., • Leaching Requirement is defined as the fraction of, irrigation water that must be leached through root, zone to keep the salinity of soil below specific limit., , •, , LR, , =, , ECiw (EC of irrigation water), -----------ECdw (EC of drainage water)
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Management, •, •, •, •, , Physical methods for amelioration, Hydro-technical methods for amelioration, Chemical methods for amelioration, Biological methods for amelioration
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Physical methods, • Deep ploughing: Helps to improve drainage and, facilitate transportation of salts downwards, • Sub-soiling, : Breaking of hard pan or cemented, sub-soil layer occurring at various depths to improve, drainage and facilitate transportation of salts, downwards, • Sanding : Application of sand and thorough mixing, • Scarpping of salts from the surface
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Hydro-technical methods, • Leaching- to leach the salts below the root zone, • Sufficient water must pass through the soil to, , decrease the salt content below the safe limit and, maintain proper salt and water balance.
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Chemical methods, • Application of gypsum and Leaching with good, quality water, , • Replace Na from exchange complex, suited for sodic, soils, • Application of sulphur, • Application of pyrites
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Problem, , GR of a soil having an initial ESP of 60 and final, ESP 10, CEC-30 cmole/kg is, • GR = [60-10] x 30, 100, , = 15
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Estimated efficiency of various amendments, Amendment, Amount equivalent to Gypsum, • Gypsum, 1.00, • Sulphuric acid, 0.57, • Sulphur, 0.18, • Iron sulphate, 1.62, • Lime sulphur, 0.75, • Calcium chloride, 0.85, • Aluminum sulphate, 1.29, • Pyrite, 0.63, • Pressmud, 0.77, • Lime stone, 0.58
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• Gypsum is the most economical and, commonly used chemical amendment, • One tone of gypsum is equivalent to 0.18 t, sulphur = 0.75 t lime sulphur = 1.62 t iron, sulphate.
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Biological Methods, • Addition of organic manures to soil which will improve and, action of plant roots and biological activity of soil, • Application or incorporation green manures where their, decomposition increase CO2 and organic acid content, which, will mobilize Ca by dissolving it, • Application of industrial byproducts like pressmud, • Growing of crops on problem soils and/or their incorporation, at the stage of maximum biomass productivity, • Growing of salt tolerant crops
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Lets Discuss Now.., , 100
