Abstract
A field study was conducted at Central Soil Salinity Research Institute, Karnal, India, during 1996-97 and 1997-98 on gypsum-amended sodic soils (Acquic Natrustalfs) in rice-wheat rotation to evaluate the effect of N:P:K fertilizers alone and their combined use with green manuring (Sesbania aculeata) or farmyard manure (FYM) on the balance of available P and K in the soil and their uptake by the crops. Continuous use of fertilizer P, green manuring, and FYM to the crops significantly enhanced the yields of rice and wheat and improved the available P status of the soil. There was, however, no significant response to K application. Application of N reduced P concentration in rice but increased P uptake in rice crops and reduced available P status of the soil. The effect of single or combined use of inorganic fertilizers and green manuring or FYM was significantly reflected in the build-up of available P and K of the soil. The contribution of the non-exchangeable K towards total K removal was about 95% in the absence of applied K which decreased to 70% with the use of K. The decrease was about 51% with the use of K combined with organic manures. Cumulative K release measured after six successive extractions was higher from the fertilizer K plus organic manures treatment compared to K fertilizer alone. The major difference was only in the first extraction representing the exchangeable K, after which release became independent of the available K of the soil.
