Validation of a Critical Nitrogen Curve for Summer Maize in the North China Plain

The concept of critical N concentration (N-c) has been widely used in agronomy as the basis for diagnosis of crop N status, and allows discrimination between field situations of sub-optimal and supra-optimal N supply. A critical N dilution curve of N-c = 34.0W(-0.37), where W is the aboveground biomass (Mg DM ha(-1)) and Nc the critical N concentration in aboveground dry matter (g kg(-1) DM), was developed for spring maize in Europe. Our objectives were to validate whether this European critical N dilution curve was appropriate for summer maize production in the North China Plain (NCP) and to develop a critical N dilution curve especially for summer maize production in this region. In total 231 data points from 16 experiments were used to test the European critical N dilution curve. These observations showed that the European critical N dilution curve was unsuitable for summer maize in the NCP, especially at the early growth stage. From the data obtained, a critical N dilution curve for summer maize in the NCP was described by the equation of N-c = 27.2W(-0.27), when aboveground biomass was between 0.64 and 11.17 Mg DM ha(-1). Based on this curve, more than 90% of the data for the N deficiency supply treatments had an N nutrition index (NNI) < 1 and 92% of the data for the N excess supply treatments had an NNI > 1.