Development of critical nitrogen dilution curve of Japonica rice in Yangtze River Reaches.

摘要

Plant-based analytical techniques of nitrogen (N) nutrition, established on the concept of critical nitrogen (N_c), can be used to diagnose the in-season N status of rice, which in turns can provide understanding of N nutrition and serve as a guide for the profitability and sustainability of agricultural production system. The objectives of present study were to develop an appropriate N_c curve for Japonica rice, to compare this curve with existing N_c dilution curve for Indica rice and to assess its plausibility to estimate the level of N nutrition for rice crop in east China. Three field experiments were conducted with varied N rates (0-360 kg N ha-1) in three Japonica rice (Oryza sativa L.) hybrids, Lingxiangyou-18 (LXY-18), Wuxiangjing-14 (WXJ-14) and Wuyunjing (WYJ) in Jiangsu province of east China. Five hills from each plot were sampled from active tillering to heading for growth analysis. The N_c dilution curve for rice, based on whole-plant N concentration, was described by the equation (N_c=3.53W-0.28), when aboveground biomass ranged from 1.55 to 12.37 t ha-1. However, for above-ground biomass <1.55 t ha-1, the constant critical value N_c=3.05% DM was applied, which was independent of aboveground biomass. Our N_c dilution curve was lower than the existing curve of Indica rice in tropics. The N nutrition index (NNI) and accumulated N deficit (N_and) ranged from 0.58 to 1.06 and 127 to -12 kg ha-1, respectively, during main development stages under different N treatments in 2010 and 2011. Different N fertilizations were suggested for unit NNI increase or unit N_and decrease at different stages. LXY-18 have more N assimilation tendency than WXJ-14 for satisfying rice growth for same dry matter. The N_c dilution curve, resulting NNI and N_and, adequately identified situations of limiting and non-limiting N nutrition and could be used as a reliable indicator of N stress during the growing season of Japonica rice in east China.