The main driving factors and responses to increase in soil available potassium in the Yangtze River basin over the past 30 years

Intensive crop rotation is one of the main causes of the continued depletion in soil potassium (K) content in the Yangtze River basin (YRB). However, recent studies have shown that soil K content is increasing in the YRB. Therefore, in this study, experimental and statistical data were collected to evaluate the soil K changes caused by K fertilizer application and straw return across the YRB. The results showed that soil available K increased, on average, by 21.7% across the YRB as a result of balanced K fertilization and an increasing proportion of straw return. From 1990 to 2019, K fertilizer input has increased from 10.1% to 24.1%, respectively. Meanwhile, from 2003 to 2011, the proportion of straw return increased by 32.8%. Considering these changes, we evaluated the effect of K fertilizer application and straw return on the soil K status. Overall, crop yield and soil available K increased by 9.9%, 7.3%, 16.3%, and 42.5%, 23.8%, and 66.4%, respectively, with K fertilization, straw return, and the concurrent use of both practices. Further, a synergistic increase in indigenous K input and soil available K alleviated the soil K negative balance and reduced the soil K fixation rate. In general, balanced K fertilization and an increasing proportion of straw return are the most vital measures for realizing the sustainable development of soil K across the YRB. The results of this research will provide useful information for sustainable K management and incentive policymaking.