Temporal and spatial characteristics of paddy soil potassium in China and its response to organic amendments: A systematic analysis

Understanding the role of organic amendments on soil potassium (K) distribution characteristics in Chinese paddy fields, we conduct a meta-analysis to explore the effect of organic amendment under different climatic and management practices. The meta-analysis consisted of 376 published papers from which 1294 paired observations were collected to evaluate the response of exchangeable K (EK) to different organic amendments in Chinese paddy soils. The results showed that EK concentration presented great variations (coefficient of variation: 44.5 %) and followed a decreasing trend from North to South and West to East, while higher EK concentration was detected in Northeast China, in 2020 s. Compared to the 2000s, the soil EK concentration in the 2020s significantly increased for the Northeast, Southwest, and East China. The highest EK concentrations were observed in Northeast (164 mg kg-1) and lowest values were observed in South China (71 mg kg-1). In case of organic amendments soil EK significantly increased compared to chemical fertilizers (CF), whereas the total K showed no significant differences in CF plus manure (CFM). The effects of organic amendments on soil K concentration revealed significant difference under various soil textures, cropping systems, and organic material types. The boosted regression trees analysis confirmed that the difference in K input for CF and CFM, and available phosphorus (AP) for straw combined with CF were the most influential variables on the variation of soil EK concentration. The structural equation modeling illustrated that organic amendments can directly and indirectly affect soil EK variation through increased K input and the regulation of crop K uptake and soil properties (total nitrogen and AP), respectively. These findings indicate that the organic amendments presented great potential for solving paddy soil K deficiency, as well as the types of organic material and soil properties should be carefully considered for greatest K use efficiency and lowest resource waste.