Density-Dependent Fertilization of Nitrogen for Optimal Yield of Perennial Rice

In the absence of tillage, perennial rice is an innovation and supplement to rice production. Proper N fertilizer application connected to planting density has been proposed as an effective way to improve rice yields. The tradeoff between crop N uptake and N supply is essential for optimal N management and soil environment benefit in the perennial rice cropping system. To assess the response of perennial rice to N fertilizer and planting density, field experiments with four consecutive growing seasons within two years, from 2016 to 2017, were conducted in southern China. Four nitrogen rates (N0, N1, N2, and N3 refer to 0, 120, 180, and 240 kg N ha(-1), respectively) combined with three planting densities (D1, D2, and D3 refer to 100 x 10(3), 167 x 10(3) and 226 x 10(3) plants ha(-1), respectively) were designed. The results showed that both N rate and planting density significantly affected crop production (p < 0.05), N uptake and soil N balance. Specifically, the N2D3 mode could achieve sustainable and higher dry matter accumulation (15.15 t ha(-1)) and grain yield (7.67 t ha(-1)) among all the treatments over the four seasons. A positive relationship between N uptake and dry matter/grain yield was observed. The N2D3 mode showed significantly higher N uptake (201 kg ha(-1) each season) and less soil N loss (27.1%), relative to C.K. Additionally, the N2D3 mode could reach the optimal N balance (-0.2 kg ha(-1)) with a low N requirement (23.9 kg N Mg-1 grain), resulting in higher N use efficiency (NAE: 26.5 kg N kg(-1), NRE: 64.9%). In the perennial rice cropping system, therefore, 180 kg N ha(-1) integrated with 226 x 10(3) plants ha(-1) could deliver higher grain yields with less N requirement, higher N use efficiency and less soil N loss. This optimal combination between planting density and nitrogen rate can result in soil N balance for sustainable perennial rice production.