New Critical Nitrogen Curve Based on Leaf Area Index for Winter Wheat

Abstract

Accurate forecasting of N required for plant growth can help optimize grain yields, farm profits, and N use efficiency and reduce the risk of environmental pollution. The objectives of this study were to: (i) establish a critical N (Nc) dilution curve for winter wheat (Triticum aestivumL.) based on the leaf area index (LAI), (ii) compare this curve withNcdilution curves for winter wheat that are based on plant dry matter, and (iii) assess the plausibility of using this new curve to estimate the N status of winter wheat. Four field experiments were conducted with different N application rates. Twenty plants from each plot were sampled from the Feekes 3 to the Feekes 10.5 stage for growth analysis. The relationship betweenNcand LAI could be described by a negative power equation,Nc= 4.06LAI−0.4, when the LAI values were in the range of 1.4 to 7.5. For LAI values <1.4, however, the constant valueNc= 3.58% was used. The N nutrition index (NNI) ranged from 0.34 to 1.31 during the vegetative stage under different N application rates from 2009 to 2011. There was a significant positive relationship between differences in NNI and differences in N application rates across four wheat development stages. Validation of the models with independent data produced a root mean squared error of 28 kg ha−1. TheNcdilution curve identified limiting and nonlimiting wheat N status and could be used as a reliable indicator of in‐season N stress of wheat grown in eastern China.