N Balance and Requirements Under Different N Management Practices in a No-Till Perennial Rice Cropping System

Abstract Aims: In the absence of tillage, perennial rice is an innovation and supplement to rice production. Evaluating crop N uptake and N requirements and maintaining soil N balance are essential for informing decisions regarding optimal N management and the accessibility of the soil environment benefits of perennial rice cropping systems. Methods: To assess the soil nitrogen cycle and balance, formulate optimal N fertilizer management for perennial rice, a field experiment with four nitrogen rates (N0, N1, N2 and N3 refer to 0, 120, 180 and 240 kg N ha-1, respectively) integrated with three planting densities (D1, D2 and D3 refer to 100×103, 167×103 and 226×103 plants ha-1, respectively) was conducted for two years over four seasons (2016-2017) in southern China. Results: The results showed that N2D3 mode could sustainably produce higher dry matter accumulation (15.15 t ha-1) and grain yields (7.67 t ha-1) over four seasons, showed significantly higher N uptake (201 kg ha-1 each season) and less soil N loss (27.1%). Additionally, the N2D3 mode could reach the optimal N balance (-0.2 kg ha-1) in perennial rice fields with low N requirements (23.9 kg N Mg-1 grain), resulting in higher N use efficiency (NAE: 26.5 kg N kg-1, NRE: 64.9%). Conclusion: In the perennial rice cropping system, 180 kg N ha-1 integrated with 226×103 plants ha-1 resulted in higher grain yields with lower N requirements, higher N use efficiencies, and lower soil N losses, thereby maintaining the soil N balance for sustainable perennial rice production.