JIANG Peng, XIONG Hong, ZHANG Lin, GUO Xiaoyi, ZHU Yongchuan, LIU Mao, CHEN Lin, XU Fuxian
To clarify the effects of different nitrogen regulation on grain yield and nitrogen use efficiency of super rice under the condition of direct seeding, a field experiment with ordinary inbred and hybrid, and super inbred and hybrid rice cultivars was conducted in Deyang City, Sichuan Province in 2016. Three different nitrogen (N) treatments and a control were set in this study including non-N treatment (N0), farmers' fertilizer practice (N1, for N1 treatment, four concentrations of 60, 60, 60, and 45 kg·hm-2 were applied at basal, three-leaf seedling stage, mid-tillering and panicle initiation, respectively), and site-specific N management (N2 and N3, for N2 treatment, 30, 60, 45, 30, and 15 kg·hm-2 were applied at basal, three-leaf seedling stage, mid-tillering, panicle initiation and heading, respectively; for N3 treatment, 30, 60, 45, and 15 kg·hm-2 were applied seedling stage (three leaves), mid-tillering, panicle initiation and heading, respectively). The grain yield, yield components, N uptake, N distribution and N use efficiency were measured in this study. The results show that grain yield was significantly affected by cultivars. Compared with ordinary hybrid and inbred rice, the yield of super hybrid rice increased by 12.2% and 8.9%, respectively, while that of super inbred rice increased by 3.2% and 0.3% respectively. Reduced nitrogen application rate with site-specific N regulation could increase grain yield of direct seeding super rice. N2 and N3 treatments were 20.0%-33.3% less nitrogen than N1 and the yield increased by 0.2%.0.7%. The yield-increasing superiority was mainly grain number per spike, seed setting rate and harvest index. The N2 treatment has slightly higher grain yield than N3 treatment. The yield gaps between N2 and N3 treatments were attributed to the differences in panicles per m2 and biomass production. Compared with the N1 treatment, the N2 and N3 treatments had lower total N uptake and distribution percentage in straw, but higher N distribution percentage in filling grain. Compared with N1 treatment, the average nitrogen use efficiency (AEN), partial factor productivity of applied N (PFPN) and recovery efficiency of applied N (REN) of N2 increased by 28.9%, 25.8% and 7.0% on average, and the average N3 treatment increased by 50.8 %, 50.2%, and 13.6%, respectively. Therefore, reduced basal and three leaves N fertilizer application with site-specific N regulation as one of alternative approaches to synchronously increase the grain yield and N use efficiency in direct seeding system in Chengdu plain. The study provides a theoretical reference for optimum nitrogen regulation in super rice production under direct seeding.