Straw return cannot prevent soil potassium depletion in wheat fields of drylands

Abstract

Potassium (K) is essential for improving crop yield and quality, but it has become a forgotten nutrient in intensive agricultural systems. Fertilizer application and straw management affect crop K uptake and soil K changes, but their effects and mechanisms have not been fully elucidated. Three long-term site-fixed field experiments were conducted in K-rich soils to understand crop yield, plant K utilization, and soil K changes in response to N fertilizer rates, P fertilizer rates, and straw management in dryland winter wheat mono-cropping systems. Results showed that grain yield and grain K uptake increased by 28–43% and 17–28% at different N rates, increased by 38–64% and 35–80% at different P rates, but decreased by 17% and 16% with straw return, respectively. Grain K concentration decreased by 9–15% in applying N fertilizers, increased by 6–9% in applying P fertilizers, and showed no difference between control (straw removal) and straw return. Although straw was returned to the field in all three experiments, soil K depletion was observed with annual decline rate and deficit index of 0.8–1.8 mg kg yr−1 and 0.5–0.8 kg K t–1 for soil available K, and 9.7–16.9 mg kg yr−1 and 5.0–12.6 kg K t–1 for slowly available K, respectively. This means that straw return is insufficient to prevent soil K depletion, and supplying K fertilizer is needed. Farmer's survey findings showed that the mean K fertilizer rate in the experimental area was 31–34 kg K2O ha–1. The current K fertilizer rate could maintain an apparent K balance if all wheat straws were returned to the field, but here the straw-returning rate was only 20–25%. Improving the straw-returning rate and managing K fertilizer rationally will be a crucial strategy for sustainable wheat production.