Fertilizer-N Application and Rice Straw Incorporation Impacts on Crop Yields, Potassium Use Efficiency and Potassium Fractions in a Rice–wheat Cropping System

A field experiment was conducted for 5 years with four fertilizer-N rates (viz. N0, N90, N120 and 150 kg N ha−1) to rice and wheat and two rates of rice straw (RS) incorporation (RS0 and RS10; 0 and 10 Mg ha−1) in wheat arranged in a randomized complete block design to evaluate the effects on crop yields, potassium (K) use efficiency and K transformations in a sandy loam soil under a rice–wheat system (RWS). Rice straw incorporation combined with fertilizer-N application significantly (p< 0.05) increased the rice and wheat yields by ~7.2 and 3.1% as compared to no-RS (RS0), respectively. These results showed that the amount of K required to produce 1 Mg of grain yield estimated as RIUEK varied between 25.6 and 32.6 kg (Mg grain yield)−1 for rice and 20.3 and 25.1 kg (Mg grain yield)–1 for wheat. The combined RS incorporation and fertilizer-N application (N120RS10) significantly decreased the RIUEK by ~14.7 and 12.9% for rice and wheat, respectively, compared with fertilizer-N application alone. The increased crop yield, K uptake and K use efficiency (PFPK and RIUEK) were significantly related to K enrichment in water soluble-K (WS-K), exchangeable-K (Ex-K) and nonexchangeable-K (Non Ex-K), 1 N hydrochloric acid extractable-K (HCl-K), lattice-K and total K fractions by ~4.1, 2.5, 6.7, 1.4, 1.6 and 1.6 times, respectively, due to fertilizer-N application and RS incorporation, compared with fertilizer-N application alone. Rice straw incorporation before wheat establishment exerted a greater impact in terms of enhanced crops' yield and K use efficiency of succeeding rice crop grown in an annual RWS.