Potassium Fractions of Soils of SASRD Research Farm of Nagaland University and Response of Soybean to Potassium

Abstract

Soil samples (21 each from surface and sub-surface) were collected from School of Agricultural Sciences and Rural Development (SASRD) Research Farm of Nagaland University, Medziphema, Nagaland and analyzed for some important physicochemical properties and different forms of potassium (K). Soils were strong to moderately acidic in reaction and quite low in total soluble salts. Sub-surface soils had slightly higher pH than surface soils. On average, the soils were high in organic carbon (OC) and low in available nitrogen (N) and phosphorus (P) contents. Higher values of OC and available N and P were recorded in surface soils. Average values of various fractions of K viz., available K, water soluble K, exchangeable K, HNO3 extractable K, non-exchangeable K, 0.01M CaCl2-K and total K in surface and sub-surface soils were 171 and 165, 12.4 and 9.2, 159 and 156, 879 and 918, 723 and 736, 24.0 and 25.0, and 5119 and 4972 mg kg−1, respectively. Available K, water soluble K, exchangeable K, 1N HNO3-K, non-exchangeable K and 0.01 M CaCl2-K constituted 3.3, 0.2, 3.1, 17.2, 14.1 and 0.5 per cent in surface soils and 3.3, 0.2, 3.1, 18.5, 14.8 and 0.5 per cent in sub-surface soils to the total K, respectively. Soybean responded significantly to K application up to 27 mg kg−1 K2O. Plant height, number of pods plant−1, oil and protein contents and N, P and K contents and their uptake increased significantly with K application. Maximum grain, stover and oil yields were recorded with 27 mg K2O kg−1 which enhanced grain, stover and oil yields by 59.1, 26.8 and 53.4 per cent over control, respectively.