Effects of nitrogen-reduction cultivation models on nitrogen accumulation and yield of hybrid indica rice

Objectives To assess the effects of the cultivation models on nitrogen (N) use efficiency and grain yield of hybrid indica rice under nitrogen-reduction.

Methods  The hybrid indica rice cultivar Chengyou 981 and Yixiangyou 2115 were selected as the planting materials. The conventional high-yielding nitrogen application rate (187.5 kg/hm²) with wet irrigation and 20.0×10⁴/hm² of plant density was set as the control cultivation model or treatment (T0). Other three cultivation models/treatments in the experiment were N-reduction cultivation models: 10% reduction of N application rate with wet irrigation and 20.0×10⁴/hm² plant density (mono-nitrogen reduction, T1), 10% reduction of N with wet irrigation and 24.0×10⁴/hm² of plant density (increased density under nitrogen-reduction, T2), and 10% reduction of N with alternate wetting and moderate drying irrigation, and 24.0×10⁴/hm² of plant density (controlled irrigation and increased density under nitrogen-reduction, T3). The root growth, N absorption and utilization, and grain yield of hybrid indica rice were investigated.

Results 1) Compared with the conventional high-yielding treatment (T0), the root dry weight, root α-NA oxidation and root bleeding intensity of rice in T1 were significantly reduced; the root α -NA oxidation and root bleeding intensity decreased significantly in T2; and the root growth indices in T3 were similar to T0 at jointing and heading stages, but significantly higher than T0 at maturity stage. 2) Compared with T0, the N accumulation of rice at jointing, heading and maturity stages in T1 significantly decreased, while the N accumulation at jointing and heading stages in T2 and T3 were slightly different from T0. The N accumulation during heading and maturity stages and N allocation in panicle at maturity stage were T3>T0>T2>T1. The recovery efficiency, agronomic efficiency and partial factor production of N fertilizer were T3>T2>T1, and the indices of T3 were also higher than T0. 3) The rice yield was in the order of T3>T0>T2>T1. T1 decreased yield by 6.37% compared with T0, owning to the significant decrease in effective panicle number and spikelets per panicle. T2 had a lower yield than T0, owing to the decreased effective spikelet number and 1000-grain weight; T3 had a higher yield than T0 by 1.78%, owning to the increased seed setting rate and 1000-grain weight.

Conclusions Reduction of N fertilizer input would significantly inhibit root growth and activity, affect the N uptake and accumulation of rice, and result in significant yield reduction. Increasing densities under nitrogen-reduction could effectively increase the root biomass and N accumulation of rice, but could not offset the yield loss caused by decreased effective spikelet number and 1000-grain weight. Controlled irrigation combined with increased densities and reduced N input could significantly improve root physiological activity at the middle to late stage, N accumulation and translocation from vegetative organs to the panicle of rice, nitrogen use efficiency and yield.