Rapeseed as a previous crop reduces rice N fertilizer input by improving soil fertility

Abstract

Crop rotations play crucial roles in maintaining soil fertility and crop productivity. However, crop nitrogen (N) fertilizer management under different rotation systems has not been well assessed. A total of 194 field experiments with different N application rates were conducted around the Yangtze River Basin with the objective of supporting rice N fertilizer management in rapeseed-rice (RR) and wheat-rice (WR) rotations. In the present study, a soil quality index (SQI) based on soil chemical parameters was adopted to estimate the indigenous N supply under different crop rotations. The optimum N application rate for rice in the two rotations with different SQI values was also further analyzed. The results indicated that rice yields under RR rotation were significantly higher than those under WR rotation, especially in the no N (N0) and low N (LN) treatments. The RR rotation also improved the partial factor productivity of N (PFPN). The rice yield of the N0 treatment was significantly positively correlated with the SQI value, indicating that the SQI value could be used to evaluate the indigenous N supply capacity of the soil. The SQI value of the RR rotation was 19.4% higher than that of the WR rotation. Principal component analysis (PCA) showed that soil organic matter, total nitrogen, and alkali-hydrolyzable nitrogen were the three most important factors affecting the SQI. Compared with the WR rotation, the soil organic matter, total nitrogen, and alkali-hydrolyzable nitrogen contents in the RR rotation were 24.1%, 16.8%, and 39.7% higher, respectively. With the increase in the SQI value, the optimum N application rate decreased. In soils with the same SQI value, the RR rotation required less N fertilizer input to achieve the same rice yield, and the optimum N application rate was 18.9 kg ha-1 lower than that in the WR rotation, especially in low-SQI soils. Therefore, rapeseed as a previous crop in rotation could enhance soil fertility and consequently improve rice yield, ultimately reducing N fertilizer application.