Using leaf dry matter to quantify the critical nitrogen dilution curve for winter wheat cultivated in eastern China

•The leaf Nc curve developed in this paper has not been reported in previous research.•The present leaf Nc curve was lower than the reference plant Nc curve.•There was a significant positive relationship between NNI and N applications.•The leaf Nc curve can be used to diagnose the N status of winter wheat in eastern China.

Accurate measurement of the nitrogen (N) required for plant growth helps optimize grain yield, farm profits, and N-use efficiency. Critical nitrogen (Nc) curves have been developed to describe N dilution in plant tissues during crop growth and to estimate the N status of whole plants; however, Nc curves for leaves have yet to be constructed. We constructed and validated a leaf Nc curve for winter wheat based on leaf dry matter (LDM) and compared it with published whole-plant Nc curves to explore the potential for estimating leaf N status of winter wheat in eastern China. Four field experiments were conducted using a range of N fertilization levels (0–375 kg ha−1) applied to six wheat cultivars in eastern China. For our growth analyses, we determined LDM and leaf N concentration (LNC) in the developmental phases from spring regrowth to heading. The leaf Nc curve fit the following relationship: Nc = 3.05LDM−0.15 when LDM ranged from 0.52 to 2.64 t ha−1. However, when LDM was <0.52 t ha−1, we applied a constant leaf critical value of 3.37%. The curve we constructed was lower than the reference whole-plant Nc curve. The N nutrition index (NNI) ranged from 0.34 to 1.31 during the vegetative stage across the 2009–2011 seasons. There was a significant positive relationship between the difference values of NNI (ΔNNI) and N (ΔN) applications over the four wheat developmental stages. We obtained a root-mean-squared-error (RMSE) of 24.53 kg ha−1 between the predicted and observed ΔN values when testing the models with independent data. The leaf Nc dilution curve correctly identified N-limiting and non-N-limiting statuses and may be used as a reliable indicator of N stress during the growing season of winter wheat in eastern China.