Maize Response to Time of Nitrogen Application as Affected by Level of Nitrogen Deficiency

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Abstract
Fine tuning current best nitrogen management practices, such as delayed N application to maize (Zea mays L.), is needed to improve fertilizer recommendations. This study was conducted to determine the relationship between relative maize N deficiency and time of N application. Levels of N deficiency were established by applying different rates of N fertilizer. Additional N was applied to each level of N deficiency at eight growth stages ranging from early vegetative growth to late reproductive growth. Chlorophyll meter readings were taken before each N application as a measure of maize N deficiency. A N sufficiency index (SI) was calculated based on the relationship between N‐deficient and non‐N‐deficient maize. Delaying N application to the six‐leaf stage resulted in nearly a 12% decrease from maximum grain yield when the SI was below 0.90, indicating N deficiency can be severe enough to prevent full recovery when N is side dressed. The greater the N deficiency, the earlier N had to be applied to obtain maximum grain production. Grain yield was increased from N application as late as R3 stage for extremely N‐deficient maize, but maximum yield was not obtained. Grain yield was depressed when N was applied at R3 for slightly N‐deficient maize. The potential benefit of late season N application depends on the degree of N deficiency. A predictive function was developed in order to determine if N fertilizer application would be warranted given the SI and time of N application.