基于叶面积指数构建滴灌玉米营养生长期临界氮稀释曲线

明确宁夏引黄灌区基于叶面积指数(leaf area index,LAI)的滴灌玉米临界氮稀释曲线模型及其适用性,探讨以氮营养指数(nitrogen nutrition index,NNI)为监测指标对滴灌水肥一体化模式下玉米氮素营养状况诊断的可行性。该研究于2017-2018年开展了不同施氮量(0~450 kg/hm^2)下4个田块的试验,采用系统分析和统计建模的方法,分析了LAI和植株氮浓度(plant nitrogen concentration,PNC)的定量关系,构建和验证基于LAI的临界氮稀释曲线模型,并建立理论框架,将基于LAI的临界氮曲线与基于植株干物质(plant dry matter,PDM)的临界氮浓度曲线关联,比较基于LAI和PDM的临界氮曲线之间的差异。结果表明,玉米营养生长期临界氮和LAI符合幂函数关系,拟合模型的评价指标均方根误差(root mean square error,RMSE)和标准化均方根误差(normalized RMSE,n-RMSE)的结果分别为0.09和4.13%,模型具有较好的稳定性。在试验氮素水平范围内,不同生育时期NNI随施氮量的增加而增加,变化范围为0.53~1.34,NNI可以准确地反映滴灌玉米氮素营养状况。在非限氮处理下,玉米植株氮素吸收与LAI成正比,LAI与PDM的异速生长参数接近理论值2/3。构建的基于LAI的临界氮曲线可以有效地识别玉米拔节期至吐丝期植株所需的氮状态,为宁夏滴灌玉米氮肥精确管理提供了一种新的评价方法。

Critical nitrogen dilution curve of drip-irrigated maize at vegetative growth stage based on leaf area index

Nitrogen is a main nutrient element for crop growth but the appropriate nitrogen application and management is important in the Yellow River Irrigation Area of Ningxia. So, an effective method of accurate nitrogen assessment for maize is urgently needed in this area. In this study, based on leaf area index(LAI) of maize under drip-irrigated system, a critical nitrogen dilution curve model was established and its applicability for nitrogen management was assessed. The feasibility of diagnosing nitrogen nutrition status of maize under a water and fertilizer drip-integrated mode by using nitrogen nutrition index(NNI) was also evaluated. Six nitrogen application rates with three replicates each were designed including 0(N0)、90(N90)、180(N180)、270(N270)、360(N360), and 450(N450) kg/hm^2 in 2017 and 2018. The LAI, dry matter and nitrogen concentration were determined at jointing stage, trumpet stage, large trumpet stage, tasseling stage, and silking stage,respectively. Then, the quantitative relationship between LAI and plant nitrogen concentration(PNC) were analyzed.Moreover, the critical nitrogen dilution curve model based on LAI was constructed and verified after analysis of aboveground biomass accumulation and plant nitrogen concentration of maize from jointing stage to silking stage under different nitrogen application rates. The critical nitrogen dilution curve model was employed to reveal the effects of nitrogen application rates on NNI of maize at different growth stages. A theoretical framework was established to reveal the relationship between LAI and plant dry matter(PDM) curves and to compare the differences between critical nitrogen curve based on LAI and that based on PDM. The results showed that, as a whole, both LAI and plant nitrogen concentration were increased as nitrogen application rate increased. However, they increased with two distinct periods, which could be classified into nitrogen limitation and nitrogen non-limitation periods. The relationship between critical nitrogen and LAI conformed to a power function model at the vegetative growth stage of maize. Meanwhile, the root mean square error(RMSE) and normalized root mean square error(n-RMSE) of this established model were 0.09 and 4.13%, respectively. It indicated this model presented a good stability to predict critical nitrogen concentration of maize as well as to evaluate plant nitrogen nutrient at the vegetative growth stage. Furthermore, the NNI increased from 0.53 to 1.34 when the nitrogen fertilizer application rate increased at different growth stages. Hence, NNI could accurately reflect the nitrogen nutrition status of maize, and 270 kg/hm^2 was the best application rate of nitrogen in this study. In addition, under non-limited nitrogen condition, the nitrogen absorption of maize plants presented a positive correlation with LAI and the allometric growth parameters of LAI and PDM were closer to two thirds of the theoretical value. In conclusion, the established critical nitrogen curve based on LAI can effectively identify the nitrogen condition required by the plant from the jointing stage to the silking stage. The critical nitrogen curve based on leaf area index provides an effective evaluation method for precise nitrogen management of maize under drip-irrigated system in Ningxia.