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

Abstract

The critical nitrogen (Nc), 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 Nc dilution curve based on leaf dry matter (LDM) 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 (0–360kgNha−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 Nc dilution curve on leaf N concentration was described by the equation Nc=3.76W−0.218, when LDM ranged from 0.67 to 4.25tha−1. However, for LDM<0.67tha−1, the constant critical value Nc=4.09%LDM was applied. This Nc dilution curve on LDM 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 (Nand) of leaves ranged from 0.65 to 1.06 and 79.62 to −6.39kgha−1, respectively, during main growth stages under varied N rates in 2010 and 2011. The results indicate that the present Nc dilution curve and derived NNI and Nand 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.