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

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 (Ouzo 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. (C) 2013 Elsevier B.V. All rights reserved.