Abstract:【Objective】 Upland soil, as an important type of arable land in China, plays an extremely important role in national food security and stability. Since the reform and opening of China, there were many great changes in farmers' fertilization patterns and planting habits because of soil testing formula fertilization, straw returning and fertilizer reduction to increase efficiency. However, there is still a lack of systematic research on the effects of these changes on the input of potassium (K) fertilizer and soil K in the main dry-farming grain of China. Therefore, the objective of this study was to evaluate the evolution characteristics of K input and fertility in major wheat and/or maize production regions of the whole country, which will clarify the present situation of K fertility and provide certain theoretical guidance for rational application of K fertilizer in different regions. 【Method】 This study was based on the National Cultivated Land Quality Monitoring database, which was from the Center of Cultivated Land Quality Monitoring and Protection, Ministry of Agricultural and Rural Affairs. Then, the K fertilizer input, soil available K (AK) and slowly available K (SAK) contents were analyzed in five regions of China, which included Northeast of China(NEC), North of China (NC), East of China (EC), Northwest of China (NWC), Southwest of China (SWC) during 1988—2007 and 2008—2018. Meanwhile, the effects of soil AK on SAK were also discussed. 【Result】 There was a relatively stable chemical K, straw K, and total K fertilizers (K2O) input in the whole country during 1988—2018, with 125 kg·hm-2·a-1, 148 kg·hm-2·a-1, and 273 kg·hm-2·a-1, respectively. There was no significant change for K input during 1988—2007 and 2008—2018. In different regions, it was observed that K input in NC and NEC regions was significantly higher than that in other regions. Compared with those of 1988—2007, the total K input in NEC, NC, EC, and SWC regions was increased during 2008—2018 by 4.22%-23.8%, while it was decreased slightly in the NWC region. The AK and SAK of the whole country were 139 mg·kg-1 and 665 mg·kg-1, respectively. Compared with 1988—2007, the AK and SAK during 2008—2018 increased by 15.1% and 6.72%, respectively. The order of soil AK in the different regions was higher in NWC and NEC regions (more than 150 mg·kg-1), lower for NC and EC regions (136-149 mg·kg-1), and lowest for SWC region (116 mg·kg-1). During 2008-2018, soil AK in NC, EC, NWC and SWC regions was increased more than during 1988-2007 by 15.7%, 17.7%, 4.16% and 34.5%, respectively. Also, the soil SAK was increased by 8.95%, 2.15%, 5.71% and 4.19%, respectively. In the main dry-farming food soils of the whole country, the relationship between soil AK and SAK could be fitted by a linear equation. With the increase in soil AK, the growth rate of soil SAK in 2008—2018 (14.2 mg· kg-1) was significantly higher than 1988—2007 (7.23 mg·kg-1). Meanwhile, the fitting equations among different regions in 1988—2018 also showed that the growth rate of soil SAK in NEC, EC and NWC regions was significantly higher than that in the NC region. 【Conclusion】 On the long-term monitoring platform of farmlands in China, compared with 1988—2007, the AK and SAK of main dry-farming grain soil were increased significantly during 2008-2018, and there was an increasing trend in most regions. Also, there was a significant linear relationship between soil AK and SAK. These results should provide a technical reference for the rapid estimation of SAK content even though there were differences in the fitting equations during different experimental periods and regions. Thus, it is recommended that different areas should accurately classify soil K supply capacity through AK and SAK by local conditions since it would establish the foundation for realizing the goal of storing K in the soil.