Morpho-electrochemical characterisation and nature of soil acidity as influenced by topography and vegetation in some acid soils of Kamrup district, Assam.

摘要

Some acid soils (Utisols and Alfisols) representing Kamrup district, Assam, India, were studied to characterize the nature of soil acidity, electro-chemical properties and their variations as influenced by topography (slope) and vegetation (forest).The positive difference between pH (H2O) and pH (KCl) reflected appreciable amount of reserve acidity in all the pedons. Organic carbon content varied from 3.0 to 13.1 g kg-1 of soil, wherein the highest being recorded under moderately thin forest vegetations with 3-5% slope. Cation exchange capacity (CEC) as determined by three different methods was compared; showing NH2OAc-CEC and effective-CEC (ECEC) as the best method in acid soils. Lime requirement was positively correlated with % Al saturation, exchangeable and extractable acidity (r=0.874, 0.962 and 0.788), respectively, the highest value (5.4 tonnes ha-1) being recorded in moderately sloped soft having lower soil pH. Exchange acidity varied from 1.00 to 4.00 cmol (p+) kg-1 and contributed 13.4to 30.1% of the extractable acidity. Extractable acidity ranging from 7.1-15.0 cmol (p+) kg-1 showed positive correlations with ECEC, % Al saturation and clay content (r=0.715, 0.678 and 0.558), respectively. Major portion of the total potential aciditywas pH dependant (69.9 to 86.5%) that varied from 6.1 to 11.25 cmol (p+) kg-1. Effect of topography and vegetation on exchange acidity was negligibleil.