Relationships between Grain Nitrogen Concentrations and the Nitrogen Status of Corn
Grain analysis is frequently used to determine the N status of corn (Zea mays L.). The objective of this study was to assess the reliability of N concentration in grain as an indicator of the N status of corn. The study involved 12 site-years of data, each having 10 rates of N applied preplanting. Nitrogen concentrations in grain tended to increase with increases in rates of N application. Nitrogen concentrations also tended to increase with increases in relative yields, but the relationships often were C-shaped, and there was no basis for establishing critical N concentrations. The relationships between N concentrations in grain and adjusted rates of N fertilization (i.e., rates of fertilization expressed relative to economic optimum) were statistically significant, but they had low predictability. For example, only 19% of the variability in N concentrations could be explained by a model that considered only data between ± 100 kg N ha−1 from economic optimum rates of fertilization. Only 1% of the variability could be explained by a model that considered only data between ±50 kg N ha−1 from economic optimum. These observations indicate that, especially where the availability of N is near or above optimal, N concentration in grain does not provide a reliable indicator of the N status of corn.
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