Rice Yield and Nitrogen Use Efficiency: Different Responses to Soil Organic Matter between Early and Late Rice

Purpose: Soil organic matter (SOM) is essential for crop production and serves as a critical indicator for soil fertility. A large deal of research has shown a large increase in the SOM content of rice fields in southern China. However, the responses of rice yield and fertilizer nitrogen (N) fate to the increased SOM remain unclear. The objective of the present study is to investigate the responses of rice yield and N use efficiency to SOM in a double-cropped rice system in subtropical China. Methods: A 2-year field experiment was conducted on three paddy fields with low, medium, and high SOM content (corresponding to a SOM concentration of 20.3, 28.5, and 37.7 g kg− 1, respectively) to examine the responses of rice yield and N uptake to SOM. Meanwhile, 15N-labelled micro-plot experiments were carried out to clarify fertilizer N recovery efficiency, N residual in soil, and N losses to environment as affected by SOM. Results: Overall, our results showed that compared to low SOM, medium and high SOM increased rice yield by 5.4