Liang Tang tangl@njau.edu.cn

Critical nitrogen dilution curves (CNDC) have been widely used for plant N status diagnosis, N management, crop modeling, and remote sensing. The CNDC can be described by a power function of critical N (Nc) and dry matter (W) (Nc = A1·W−A2), where parameters A1 and A2 control the starting point and slope of the curve, respectively. Wheat is a major crop worldwide, and its CNDCs developed under different conditions (genotype×environment×management, G×E×M) show large parameter variations.

This study aimed to investigate the uncertainty and drivers of wheat CNDCs for organ-specific and shoot based on 23 field experiments (environments) involving different varieties, ecological sites, and years. The results show that parameters A1 and A2 are highly correlated. Although the variation of parameter A1 was less than that of A2, the values of both parameters can change significantly in response to G×E×M.

The drivers of curve parameters include maximum N concentration, maximum biomass, and accumulated growth degree days (AGDD) during the vegetative growth period and planting density. Though the Nc curve differences between G×E×M were statistically significant, the NNI differences remained relatively small.

NNI calculated using organ-specific CNDC is in general consistent with NNI estimated with overall shoot CNDC, indicating that a simple organ-specific CNDC may be used for wheat N diagnosis to assist N management. However, the significant differences in organ-specific CNDC across G×E×M conditions imply potential errors in Nc and crop N demand estimated using a general CNDC in crop models, highlighting a clear need for improvement in Nc calculations in such models.

These results provide new insights into N diagnosis and management, modeling and prediction in wheat.