Development of critical nitrogen dilution curve in rice based on leaf dry matter

The critical nitrogen (N-c), defined as the minimum N concentration required for maximum growth, is proposed for diagnosis of the in-season N status in crop plants. It has been established for several crops including rice on whole-plant dry matter (DM) basis but has not been determined for canopy leaf basis. This research was undertaken to develop a new N-c, dilution curve based on leaf dry matter (L-DM) and to assess its applicability to estimate the level of N nutrition for Japonica rice in east China. Three field experiments were conducted with varied N rates (0-360 kg N ha(-1)) and 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 and leaf N determination. The N-c dilution curve on leaf N concentration was described by the equation N-c = 3.76W(-0.218), when L-DM ranged from 0.67 to 4.25 t ha(-1). However, for L-DM <0.67 t ha(-1), the constant critical value N-c = 4.09%L-DM was applied. This N-c dilution curve on L-DM basis was slightly higher than the curves on plant DM basis in Japonica rice, yet both lower than the reference curve of high yielding Indica rice in tropics. The N nutrition index (NNI) and accumulated N deficit (N-and) of leaves ranged from 0.65 to 1.06 and 79.62 to -6.39 kg ha(-1), respectively, during main growth stages under varied N rates in 2010 and 2011. The results indicate that the present N-c dilution curve and derived NNI and N-and adequately identified the situations of N-limiting and non-N-limiting nutrition in two rice varieties and could be used as reliable indicators of N status during growth of Japonica rice in east China. (C) 2013 Elsevier B.V. All rights reserved.