Crop yield and soil available potassium changes as affected by potassium rate in rice–wheat systems

Abstract

Large areas of the arable soils of the world are deficient in potassium (K) due to the low application rate of K fertilizer. However, current soil test methods cannot precisely determine soil available K changes. From 2009 to 2014, a field experiment was conducted in a rice–wheat cropping system in the Yangtze Plains using five K rates. The objectives were to determine the responses of wheat and rice yield to different K rates and to compare the soil available K changes extracted by three methods (ammonium acetate (NH4OAc), boiling nitric acid (HNO3), and sodium tetraphenylboron (NaTPB)). Long periods without application of K fertilizer markedly decreased wheat yield by 47% and rice yield by 15% compared with local farmers’ K practices (FKP, 90 and 120kgK2Oha−1 for wheat and rice, respectively). The FKP achieved optimal yields for wheat and rice; however, only 160% of FKP achieved a positive K balance for the cropping system. Soil-extractable K consistently decreased with increasing cropping rotations where the K rate was below 160% FKP for the three extraction methods. The extractable and changed amounts for the NH4OAC and HNO3 methods were significantly lower than that for the NaTPB method. The soil K changes for NaTPB were closer to the theoretical soil available K changes (TAKC) derived from an apparent K balance. The NaTPB method could be useful for accurately determining changes in soil available K in cropping systems.