Potassium Nutrition of Rice as Influenced by Long Term Use of Fertilizers in Inceptisol

The long term fertilizer experiment was designed in Aeric Haplaquept of Bhubaneswar, Orissa with rice-rice cropping system. The treatments comprised of 100% N, NP, NPK (with and without S, Zn, FYM and Weedcide) 50 % and 150 % NPK along with control (no fertilizer) and an additional treatments receiving lime+NPK (based on soil test). In the preceding years substantial yield reductions of kharif rice were observed in the treatment receiving either to K or low rates of K application. Moreover, K balance sheet was found to be negative in all the treatments. In spite of negative K balance there was gain of NH₄OAC extractable K from 10 to 30 kg ha^-1 and loss of non exchangeable K from 17 to 121 kg ha^-1 in all the treatments over initial value. Equilibrium activity ratio (AR Ke) was found to be the lowest 1.2 x 10^-3 (M/l)^1/2 in 100 % NP and highest (3.2 x 10^-3 (M/L)^1/2 in 150 % NPK treatment. Potential building capacity (PBC-K) was highest in the treatment receiving lime + NPK (soil test). Labile K (-DKe) was lowest (2.2 x 10^-2 meq/100 g) in 100 % NP treatment as against 3.4 x 10^-2 meq/100 g in the treatments receiving lime + NPK (soil test). K/N ratio of plant was much lower at the PI stage and also decreased with increasing levels of NPK which showed that K availability was not in proportion to availability of N. K/Fe ratio increased 2 to 3 fold and there was also increase of Mn/Fe ratio of PI stage with increasing levels of K. Variations in K content in plant were found to be significantly related to the variation in equilibrium concentration of K, ARKe, NH₄ OAC-K and HNO₃-K. Fe content in plant decreased with increasing levels of K application. Yields were significantly higher with higher levels of K.