Climate, Management, and N Effect on Corn Leaf N, Yield, and Grain N

Two field corn (Zea mays L.) N response experiments, with previous cropping of alfalfa (Medicago sativa L.) and wheat (Triticum aestivum L.), were conducted for 4 years (1977 to 1980) on Mexico silt loam (fine, montmorillonitic, mesic Udollic Ochraqualf). The study was conducted to relate the climatic factors of air temperature in June, July, and August, expressed as heat units, and precipitation during the same months to corn yield response to fertilizer N. A previous evaluation utilized grain N (a quantitative measurement) as measure of plant N sufficiency to develop a model integrating these climatic factors to predict total Nand fertilizer N requirements. The objective of this study is to integrate the variables of fertilizer N application by leaf N (a relative plant nutrient measurement) concentration with climatic parameters to predict N requirements for maximum yield. Regression analyses related relative yield to monthly precipitation, heat units, and their products of leaf N or applied N and the square of leaf N or applied N. The primary N source affecting leaf concentrations was from fertilizer N when corn followed wheat and from the previous crop residue when corn followed alfalfa. The critical leaf N concentration of 2.09 mol kg⁻¹ was selected when relative yield of 97% was achieved, because additional increases in leaf N had little effect on yield. Precipitation and heat units accounted for 32 and 62% of the ear leaf N concentration when corn followed wheat and alfalfa, respectively. Including linear and quadratic terms of fertilizer N explained 98 and 92% variability, respectively, in the leaf N, and the fertilizer N requirements for yield maximization were calculated to be 152 and 66 kg ha⁻¹ where corn followed wheat and alfalfa, respectively. This corresponded to 137 and 48 kg N ha⁻¹ fertilizer requirements when 1.09 mol kg⁻¹ grain N was used as the criterion for maximum yield. The summation of precipitation and heat units into the monthly periods of June, July, and August were significantly related to leaf N and grain N. Results indicate that leaf N concentration as well as grain N, can be used as a tool to quantify the N sufficiency and N fertilizer requirements for maximum corn yield.