SS_Problem Soil

• Slow permeable soils


  Mainly due to very high clay content, infiltration rate < 6cm/day, so more runoff which eventually leads to soil erosion and nutrient removal
• Slow permeable soils

  • Capillary porosity is high, leading to impeded drainage, poor aeration and reduced conditions
• Measures to increase soil permeability

  • Addition of organic matter
  • Formation of ridges and furrows
  • Formation of broad beds (3-9 m wide)
• Soil 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.
• Soil crusting

  Predominant in Alfisols but also occur in other soils too
• Measures to reduce soil crusting

  • When soil is in optimum moisture regime, ploughing should be done
  • Lime or gypsum @ 2 t ha-1 may be uniformly spread and another ploughing 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
• Soil acidification


  A natural consequence of chemical mineral weathering promoted by soil respiration and leaching in humid climates
• Soil acidification


  Common in well-drained areas where precipitation exceeds evapotranspiration and causes loss of base cations
• Soil acidification

  Caused of accumulation of soluble inorganic and organic acids at a faster rate that they can be neutralized
• Soil acidification induced by human activities

  • Improper irrigation
  • Increase nitrogen and sulfur inputs
  • Industrial and mining activities - acid produced from pyrite oxidation and from acid precipitation caused by emission of sulfur (S) and nitrogen (N) gases
• Processes that causes soil acidification

  • Sources of Hydrogen (H+) ions: Carbonic and other organic acids - Carbonic acid (H2CO3) formed when CO2 dissolves in water, high levels of CO2 in the soil air from root respiration and decomposition of SOM, Citric acid, malic acid (weak acids), carboxylic and phenolic acids (stronger and complex), from breakdown of OM
  • Accumulation of Organic matter - formation of soluble complexes with nonacid nutrient cations such as calcium and magnesium which lead to leaching, OM is source of H+ because it contains numerous acid functional groups which these ions dissociates
  • Oxidation of Nitrogen (nitrification) - process produces dissociated nitric acid, Oxidation of sulfur - from FeS2 (pyrite), process produces dissociated sulfuric acid, Acids in precipitation, Plant uptake of cations
• Acid rain


  Acid vapors, primarily sulfuric and nitric, form in the atmosphere as a result of emission of sulfur dioxide (SO2) and nitrogen oxides from natural and anthropogenic sources
• Acid rain


  Largest anthropogenic sources of these gases are from the burning of fossil fuels (source of sulfur gases), smelting of sulfur-containing metal ores, and exhaust of motor vehicles (source of nitrogen oxides)
• Acid rain


  These vapors condense to form aerosol particles and, along with basic materials in the atmospheric water, determine the pH of precipitation
• Acid rain


  Major cations in precipitation water are H+, NH4+, Na+, Ca2+, Mg2+ and K+ while the major anions are SO42-, NO3- and Cl-
• Ave. value for amount of H+ produced per year from acid rain falling on industrialized areas is 1kmol H+ per ha per year
• Acid sulfate soils

  Have very low pH due to the oxidation of pyrite, occurring in marine flood plains and coastal marshes in temperate and tropical areas
• Acid sulfate soils are estimated to occupy an area of at least 24M has worldwide
• Acid sulfate soils


  When they are drained and pyrite oxidation occurs, extreme acidity is produced
• Complete oxidation of pyrite (FeS2)

  FeS2 + 15/4O2 + 7/2H2O Fe(OH)3 + 2H2SO4
• Acid sulfate soils


  The high concentration of sulfuric acid cause pH as low as <4, causing dissolution of clay minerals thus releasing soluble aluminum
• Management of acid sulfate soils

  • Prevent the S oxidation
  • Sulfide-bearing wetland soils are best left undisturbed or maintained under saturated, wetland-like conditions
• Effects of soil acidification

  • Leads to alteration of soil osmotic potential, restriction on plant water intake, reduced microbial activity, toxicity of ions (e.g. chloride and sulphate)
• How to manage soil acidity

  • Liming
  • Gypsum application
  • Planting of Salt tolerant Crops
  • Use of organic matter
• Liming


  Liming materials (in either oxide, hydroxide or carbonate form) react with carbon dioxide and water to yield bicarbonate when applied to acid soil
• Reaction of liming materials

  CaMg(CO3)2 + 2H2O + 2CO2 <==> Ca + 2HCO3- + Mg + 2HCO3-
• Liming


  The Ca2+ and Mg2+ replace H+ and Al3+ on the colloidal complex
• Gypsum


  Gypsum (CaSO4 . 2H2O) is a widely available material from natural deposits or as an industrial by-product, a neutral salt that does not raise soil pH and so does not increase CEC
• How does gypsum work?

  Can ameliorate Al toxicity without increasing soil pH, Ca from surface applied gypsum moves down the soil profile more readily than that from lime, the released Al is thought to react directly or indirectly with the sulfate ion (AlSO4- ions are non-phytotoxic)
• Soil/cultural management for salt-affected soils

  • Planting the seed in the center of the raised bed / ridge may affect the germination as it is the spot of greatest salt accumulation
  • A better salinity control can be achieved by using sloping beds with seeds planted on the sloping side just above the water line
  • Alternate furrow irrigation is advantageous as the salts can be displaced beyond the single seed row
  • Application of straw mulch had been found to curtail the evaporation from soil surface resulting in the reduced salt concentration in the root zone profile within 30 days
• How to manage soil acidity using organic matter

  High MW organic matter can bind tightly with Al ions and prevent them from reaching toxic concentrations in the soil solution, Low MW organic acids from microbial decomposition and root exudation can form soluble complexes with Al ions that are non-toxic to plants and microbes, Many organic amendments contain high amounts of Ca held in organic complexes that leach readily down the soil
• Salt-affected soils

  Widely distributed around the world, typically in areas with precipitation-to-evaporation ratios of 0.75 or less, and in low, flat areas with high water tables that may be subject to seepage from higher elevations
• Salt-affected soils cover approx. 7% of earth's total land area, about 23% of its cultivated agricultural land, and almost 50% of its irrigated land
• Development of salt-affected soils

  In most cases, soluble salts in soils originate from weathering of primary minerals in rocks and parent materials, In extremely dry regions, Ca sulfate accumulations (gypsic horizons, relatively soluble) may form near soil surface, In some cases, salts are transported to a developing salt-affected soil as ions dissolved in water; when water is evaporated, salts cannot evaporate thus left to accumulate in the soil
• Development of salt-affected soils

  Changes in local water balance (thru human activities) increase input of salt-bearing water more than they increase the output of drainage water, Increased evaporation, waterlogging, and rising water tables result
• Development of salt-affected soils in non-irrigated soils in arid and semi-arid regions

  Salts (chlorides and sulfates of Ca, Mg, Na and K) accumulate naturally in some surface soils due to insufficient rainfall to flush them out
• Possible causes of salinization in South and Southeast Asia

  • Intrusion of sea water
  • Improper irrigation methods
  • Evaporation of saline groundwater
• In 2015, experts reported that salt-affected soils are developing in certain coastal area in monsoon zones in South and Southeast Asia, mainly through saltwater intrusion
• In the Philippines with its 18,400 km long coastline, 400,000 hectares are of coastal saline soils, half of which is severely salt-affected
• Classes of salt-affected soils

  • Saline
  • Saline-sodic
  • Sodic