RELATIONSHIPS BETWEEN LEAF NITROGEN CONCENTRATIONS AND THE NITROGEN STATUS OF CORN

The N status of corn (Zea mays L.) often is evaluated by analyzing the leaf opposite and below the primary ear at silking. The objective of this study was to assess the reliability of leaf N concentration as an indicator of the N status of corn. The study involved 12 site-years of data, each having 10 rates of N applied preplant. Leaf N concentrations tended to increase with increases in rates of N application and with increases in grain yields. Because optimal and above-optimal rates of N application resulted in similar leaf N concentrations, however, there was little basis for defining a critical concentration of N (i.e., a concentration of N indicative of adequate but not excessive N availability). The relationships between leaf N concentrations and adjusted rates of N fertilization (i.e., rates of fertilization adjusted relative to economic optimum) were statistically significant, but they had low predictability. For example, only 16% of the variability in leaf N concentrations could be explained by a model that considered only data between +/- 100 lb N/acre from economic optimum. Overall, the results indicate that leaf N concentrations are not a sensitive indicator of the N status of corn.