Fertilizer inputs, nutrient balance, and soil nutrient-supplying power in intensive, irrigated rice systems. II: Effective soil K-supplying capacity

Abstract

Based on the analysis of soil K status in 11 long-term fertility experiments in Asia, two approaches for assessing the K-supplying power of lowland paddy soils were evaluated to predict total K uptake by irrigated rice. A regression model combining commonly used static soil test parameters that appeared to integrate measures of K release from nonexchangeable forms as well as chemical factors affecting K activity in soil solution explained 72% of the crop K uptake in NP and NPK treatments. However, this approach would require determination of six soil properties and it does not provide a direct measure of K release dynamics. The second approach used mixed-bed ion exchange resin capsules to measure K release during 2-wk anaerobic incubation. The resin method provided an integrative measure of soil K status and the factors controlling K transformation and diffusion rates, which are embodied in two kinetic parameters describing the dynamics of rapid- and slow-phase K release. The resin method was sensitive to past fertilizer history and the resulting buildup or depletion of soil K reserves and it was a better predictor of total K uptake in the NP and NPK plots (r2=0.82) than static soil tests. The results also indicated that high (Ca+Mg)/K ratios may contribute to K deficiency in rice soils.