Soil Environment and its Modification-5 Point Wise Notes for Competitive exam

Soil

• Optimum soil moisture for mineralization is 50 to 70 per cent water holding capacity of soils.

• Mineralization is temperature dependent process and rate of mineralization is more at high temperatures.

• Immediately after application of urea, it is hydrolysed in the presence of urease and forms ammonium carbonate.

• Ammonium carbonate is an unstable compound and decomposes into ammonium and carbon dioxide.

• Ammonium is adsorbed on the clay complex, a portion is absorbed by the crop and around 11% is lost as volatilization.

• Sine urea is soluble, leaching losses occur under lowland conditions.

• Mixing urea with soil and incubating for 24 to 48 hours results in conversion of urea into ammonical ion and adsorbed on complex reducing leaching losses.

• Incubating urea with soil is applicable only to acid and neutral rice soil.

• Incubating urea with soil increases volatilization in alkaline soils.

• Volatilization losses range from 0.1 to 20.0 per cent.

• Volatilization losses can be reduced by incorporation of fertilizers or by placement.

• Loss of nutrients beyond root zone along with water is known as leaching.

• Nitrate forms of nitrogenous fertilizers are subjected to higher leaching losses compared to other forms.

• Leaching losses with ammonical fertilizers are less as ammonium ions are adsorbed on clay complex.

• Leaching losses of fertilizers are more in submerged soils and in soils with less CEC.

• Nitrates present in the soil are converted into elemental nitrogen and is lost into the atmosphere.

• Denitrification losses are more in submerged soils.

• Fixation of ammonium is due to trapping of these ions within crystal lattice of montmorillonite, illite and vermiculite minerals.

• The above minerals fix more ammonium when the soil is dry due to contraction of these minerals.

• Amount of nitrogen fixed ranges from 4 to 54 per cent of total N content.

• Mineralization is faster in aerobic soils and is carried out by fungi, actinomycetes and bacteria.

• When large quantities of organic matter is added to the soils, the microorganisms utilize available nitrogen in the soils for their multiplication.

• Temporary locking up of nitrogen in microorganisms is called immobilization.

• Immobilization is reverse process of mineralization.

• Inorganic phosphorus is more in soil than organic phosphorus.

• Inorganic forms of soil phosphorus are Ca-P, Fe-P and Al-P.

• Dominant form of phosphorus in vertisols is Ca-P.

• Dominant form of phosphorus in alfisols is Fe-P.

• In Indian soils, Ca-P is around 40 to 50 per cent of total phosphorus in neutral and alkaline soils and more than 50 per cent in alkaline soils.

• Fe-P and Al-P are less than 10 per cent in these soils.

• Phosphorus in soil solution is in the form of primary and secondary orthophosphates (H2PO4- and HPO42-).

• Primary orthophosphate (H2PO4-) is more in acid soils.

• Secondary orthophosphate (HPO42-) is more in alkaline soils.

• Phosphorus in soil solution depends on rate of decomposition of organic matter and rate of reaction with inorganic fraction.

• Organic and inorganic phosphorus is in equilibrium with phosphorus in soil solution.

• Fixation of phosphorus is by adsorption, isomorphous substitution and double decomposition.

• Fixation of phosphorus is influenced by pH, nature and amount of clay, free oxides of Fe and Al, calcium carbonate and organic matter.

• Acidic soils fix more phosphates than neutral, alkaline and calcareous soils.

• At pH 2 to 5, fixation is mainly by formation of insoluble Fe and Al phosphates as Fe and Al are more in acid soils.

• Within the pH range of 4.5 to 7.5, phosphate is fixed on clay particles by replacing two hydroxyl ions from aluminium in clay with one ion of primary orthophosphate and by forming clay phosphate linkage.

• Within the pH range of 6 to 10, phosphate is precipitated as phosphates of calcium or magnesium as calcium and magnesium are more in alkaline range.

• Phosphorus fixation is more when the clay content is high.

• Vermiculite and smectite clay fixes more phosphorus than kaolinite.

• Black soils have higher fixing capacity than red soils.

• Presence of oxides of Fe & Al results in formation of sparingly soluble phosphate.

• Phosphate fixation is high in soils with high CaCO3.

• Presence of FYM shortens period of ‘P’ fixation and promotes its availability.

• Application of poultry manure decreases phosphorus availability initially, increases rapidly and attains steady state after 20 days.

• Crop production on red soils is largely limited by low availability of phosphorus, which is attributed to adsorption of phosphate by minerals including Fe and Al oxides and Kaolinite.

• Water soluble potassium is present in the soil solution as K+ ion. It is in equilibrium with exchangeable K.

• Fixed, exchangeable and soluble potassium are in dynamic equilibrium in soil.

• Unavailable K or fixed K in mica and feldspar made available slowly through weathering process.

• Iron is most abundant metal element in earth crust.

• Iron occurs as oxides, hydroxides, phosphates in primary and secondary minerals.

• Iron deficiency occurs in calcareous soils and soils with high phosphorus.

• Available and exchangeable iron decreases with increase in pH as it is inversely related to solubility of iron.

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