Maize response to time of nitrogen application as affected by level of nitrogen deficiency

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 sia-leaf stage resulted in nearly a 12% decrease from maximum grain yield when the SI tvas below 0.90, indicating N deficiency ran 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.