3 Results and Discussion
3.1 Spatiotemporal changesin soil K in the Yangtze River basin in China
Soil available K presents soil K concentration in real time, and it has been widely used to predict soil K availability and guide fertilization (Islam & Muttaleb, 2016). During 1990-2008 and 2009-2019, soil available K was 62.5-186.0 mg kg-1 (mean, 96.8) and 35.9-373.5 mg kg-1 (mean. 117.8), respectively, across the Yangtze River basin (Figure1 and Table 1). Levels of soil available K increased by -7.1%-103.4%, the increase was lower in Hunan, Guizhou, Zhejiang and Jiangsu provinces (< 10%), and higher in Anhui, Jiangxi, Henan and Chongqing provinces (> 30%). Soil available K in 2009-2019 was greatly improved compared with that in 1990-2008.