Critical grain and stover nitrogen concentrations at harvest for summer maize production in China
A uniform critical N concentration is desirable to serve as an indicator of N status and to guide agricultural practice and regulation. Our objective was to evaluate whether grain and stover N concentrations in summer maize (Zea mays L.) at harvest can serve as indicators of N status, and to determine a critical grain and stover N concentration (CGNC and CSNC) for maize production in China. At optimal nitrogen rate (ONR), grain N concentration was close to maximum, while stover N concentration was significantly lower, as calculated using a linear plus plateau model. Soil residual nitrate N content after harvest and N losses for maximum stover N concentration increased by 32 and 42 kg N ha–1, as compared to values with ONR. Based on 141 on-farm N response experimental sites, CGNC and CSNC were 12.6 ± 0.6 g kg–1 ( ± CL0.05) and 8.1 ± 0.8 g kg–1 g kg–1, respectively. An evaluation across 122 on-farm sites indicated that 70 and 66% of sites had grain and stover N concentrations less than the CGNC and CSNC at deficient (0 N control) N supply. When N was supplied in excess, 54% of sites had stover N concentrations greater than CSNC while only 14% of sites had grain N concentrations greater than the CGNC. This region wide study concluded that critical N concentrations were useful indicators of N deficiencies in maize production, but were less than reliable as indicators of excess N fertilization, in particular for grain N concentration.