Dense planting with reducing nitrogen rate increased grain yield and nitrogen use efficiency in two hybrid rice varieties across two light conditions

Abstract

Dense planting with reducing nitrogen rate (DPRN) is a sustainable strategy to improve rice yield and nitrogen (N) use efficiency. Nevertheless, the feasibility of such strategy under low light stress condition has not been examined in detail. Two field experiments and a micro-plot experiment were conducted to evaluate the performance of DPRN and sparse planting with high N rate (SPHN) under two light conditions (L0, natural light intensity and L1, 30% of L0) with two contrasting hybrid rice varieties (Yliangyou 1 and Luoyou 9348) in 2014 and 2015. In field experiments, L1 resulted in sharp decline in grain filling, 1000-grain weight, biomass, harvest index, N uptake, N use efficiency for grain production and partial factor productivity of applied N fertilizer, and consequently 41.2–53.4% grain yield loss for two varieties in comparison with L0. Interestingly, 8.6–13.5% higher grain yield, and better performance of yield components and N use efficiency were observed from DPRN than SPHN across two light conditions. In micro-plot experiment, responses of grain dry weight and yield-attributing traits to light intensity and crop managements were similar to those in field experiments. No difference was observed in N uptake from fertilizer, N recovery rate, N retention rate and N loss rate between L0 and L1, while DPRN increased N recovery rate by 14.8% and N retention rate by 35.1%, and consequently decreased N loss rate by 29.4% across two light conditions compared with SPHN. The differences in responses of grain yield and related parameters to low light stress (L1) between the two cultivars were small. These results suggest that DPRN is also feasible to increase grain yield and N use efficiency for hybrid rice varieties grown under two light conditions.