Nitrogen-Reduction in Intensive Cultivation Improved Nitrogen Fertilizer Utilization Efficiency and Soil Nitrogen Mineralization of Double-Cropped Rice

Under the current rice cropping system, excessive nitrogen application has become a major issue that needs to be changed, and nitrogen reduction has become a hot research topic in recent years. The use of optimum planting density is becoming a common agronomic management system in addition to nitrogen reduction, especially under double cropping rice systems. In this paper, changes in rice yield, nitrogen-use efficiency (NUE) and net N mineralization under dense planting with a reduced nitrogen rate (DPRN) were studied. By comparing DPRN with high-nitrogen sparse planting (SPHN), we found that the population tiller number (tiller number per unit area) increased by 9–27% under DPRN cultivation. Nitrogen accumulation under DPRN treatment of double-cropped rice was basically stable. NUE under DPRN was significantly higher by 1.3–22.7% compared to SPHN. The partial factor productivity of applied N (PFPN) was significantly higher than that of SPHN, with an increase of 4.3–22.8%. The net N mineralized of double-cropped rice under DPRN increased at different stages, and the increase in late-season rice (LSR) was greater than that of early-season rice (ESR). The highest net N mineralized in double cropping rice at different stages was found in the dense planting treatment (DP) and N2 (120 kg N h−1). In conclusion, DPRN cultivation of double-cropped rice could be accepted as a proper management strategy for reducing nitrogen input, improving NUE and promoting soil nitrogen mineralization under given conditions.