Abstract
AbstractSeeming conflict between the need to use N fertilizers and the need to protect groundwater quality requires better tools for distinguishing between fertilizer applications that are essential and those that are excessive. Studies were conducted to evaluate NO‐3 concentration in corn (Zea mays L.) stalks at physiological maturity as the basis for a tissue test to characterize degree of N excess during corn production. Samples of the lower portion of corn stalks were collected from plots in N‐rate experiments at 18 site‐years in Iowa. Observed relationships between grain yields and stalk NO‐3 concentrations indicated sharp breaks between NO‐3 concentrations that were not adequate and those that were adequate for obtaining maximum or near‐maximum yields. When yields were near maximum, stalk NO‐3 concentrations increased linearly with amounts of N fertilizer applied. Stalk samples collected at various times after black layering showed that NO‐3 concentrations remained constant for at least 2 wk. These observations suggest that stalk NO‐3 concentration offers great potential as the basis for a tissue test to characterize degree of N excess during corn production.
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