Effects of land use change on soil carbon and nitrogen in purple paddy soil

Rural land use patterns in southern China centered on household grain crop production have observed significant changes in the past few decades, profoundly affecting the release and fixation of carbon and nitrogen in the paddy soil of the region. This study selected different land use patterns developed in purple paddy soil on a decadal time scale, examined the changing rate of soil carbon and nitrogen of the purple paddy soil after abandonment, dry-farming, and fish-farming, and revealed the impact of land use changes on the balance of soil carbon and nitrogen. Results showed that the loss rates of soil organic carbon, readily oxidizable organic carbon and total nitrogen at the initial stage of dry-farming were most considerable, followed by abandonment and fish-farming. An average of 11.95-13.94 g kg-1 soil organic carbon loss and 0.90-1.03 g kg-1 total nitrogen loss of the cultivation horizon were observed when purple paddy soil was abandoned and dry farmed. In comparison, the net release of soil organic carbon and total nitrogen after fish-farming were 6.64 and -0.23 g kg-1. The changes of land use of rural area driven by rising labor cost and market demand have been inducing a continuous decline in soil C:N and significantly reducing the purple paddy soil's carbon sequestration ability. The promotion of no-tillage management, increase of organic manure application, and avoidance of over-use of nitrogen fertilizer in dryland farming need to be further considered to meet the dual pressures of China's resource constraints and carbon neutrality goals. A regression model may predict the changes in soil carbon after the change of paddy soil utilization, which provides a pathway for predicting changes in farmland carbon sequestration potential and carbon storage caused by changes in paddy soil utilization in the future.