Determination of critical nitrogen dilution curve based on leaf area index in rice

The environmental constraint caused by intensification of rice production in China has raised the need to adjust crop nitrogen (N) fertilizer requirement. Leaf area index (LAI)-based assessment of crop N status can be an effective approach to optimizing N management in rice production. This study was designed to develop a new methodology for establishing the critical nitrogen (Nc) dilution curve based on LAI, to compare if a Nc dilution curve based on LAI would allow a better diagnosis of N nutrition status than that on plant dry matter (PDM) basis and to assess its applicability for estimating plant N status in Japonica rice (Oryza sativa L) in east China. Three field experiments with varied N rates (0–360kgNha−1) were conducted using three Japonica rice hybrids, Lingxiangyou-18 (LXY-18), Wuxiangjing-14 (WXJ-14) and Wuyunjing (WYJ) in lower Yangtze River reaches. LAI and plant N concentration (PNC) were determined from active tillering to heading for growth analysis in each experiment. The LAI and PNC ranged from 0.29 to 7.46 and 0.99 to 3.11%, respectively, under the varied experiment conditions. The relationship between N uptake and LAI expansion are strictly proportional and robust across the environments. The Nc dilution curve (Nc=3.70LAI−0.35) was validated for N-limiting and non-N-limiting growth conditions. The N nutrition index (NNI) and accumulated N deficit (Nand) ranged from 0.69 to 1.06 and 88.8 to −7.54kgha−1, respectively, over main growth stages. The values of ΔN derived from either NNI or Nand could be used as references for in-season N dressing management in rice. Our results indicate that Nc dilution curve as a function of LAI efficiently identified the conditions of limiting and non-limiting N nutrition and can be adopted as a novel tool for evaluating plant N status for precision N management in Japonica rice of east China.