Long-term soil moisture evolution and its driving factors across China's agroecosystems

Water is a critical resource for sustainable development and stable food production in agroecosystems. China is one of the countries with intensified agricultural activities and extreme water shortages. Climate change is likely to contribute to an increased scarcity of agricultural water resources, which may threaten China's food security. Therefore, a comprehensive understanding of long-term agricultural soil water variation and its controlling factors at a regional scale is urgently needed. Based on in-situ relative soil moisture (RSM, the ratio of soil water content to field capacity, %) data collected from 238 agricultural stations in China, variations in RSM between 1992 and 2012 and the driving factors were investigated within different climate zones. Overall, the national mean RSM showed a decreasing trend, indicating mild or moderate levels of drought during the study period. The rates and ratios of RSM reduction varied with the soil depth and climate zone. Among the four climate zones, the reduction in RSM was faster and higher in the plateau mountain and temperate continental climate zones; however, there was no significant trend in the temperate humid and subtropical humid climate zones. Both climate and agricultural management activities have made significant contributions to RSM in China's agroecosystems. In this study, RSM in 58.2% of the selected stations was driven by the combined effects of climate and management activities. For different climate zones, the RSM in the plateau mountain and temperate continental climate zones was mainly controlled by temperature and precipitation, respectively. In the temperate humid climate zone, climate change was the dominant factor controlling RSM. In the subtropical humid climate zone, grain output had a negative effect on the RSM. Our findings provide a theoretical reference for each region to facilitate agricultural water evaluation and agricultural policymaking, and enhance field management for the sustainable use of agricultural water resources.