Maize nitrogen utilization and nitrate leaching modeling in Togo and New York

More experimental work and continued development and use of mathematical models are needed to efficiently address both economic and environmental issues related to fertilizer nitrogen (N) use.; Two separate experiments were conducted in New York and Togo. The experiment in NY was conducted to calibrate and validate the LEACHMN model using field data including soil hydraulic and chemical properties, water flow rate and volume, soil profile NO₃-N, NO₃-N leaching losses, and maize N uptake collected from a three-year nitrate leaching experiment conducted on two soil types. In Southern Togo, the experiment was conducted to (1) identify the appropriate rates and timing of fertilizer N application that optimize fertilizer use and maize yield, (2) quantify the effects of rate and timing of N application on nitrate leaching potential and N mass balance, and (3) calibrate, and validate the LEACHMN model.; Under the conditions of NY, LEACHMN accurately predicted water flow rate and drainage volume. This capability of the model resulted from the fact that the input parameters of hydraulic conductivity and soil water retention were collected on-site from undisturbed cores and reflected the somewhat well structured, macropore-influenced water flow patterns of the experimental sites. When calibrated for each year, soil type, and N treatment, the model accurately predicted mass NO₃-N in the soil. However, slight discrepancies occurred between simulated and measured data because the model inaccurately predicted maize N uptake. Using calibrated N transformation rates for each year-treatment combination and soil type, LEACHMN satisfactorily predicted NO₃-N leaching losses. The use of three-year average rate values was satisfactory only where the rates were similar to those used in the calibration sets at each site, indicating that both year and soil type effected the N transformation rates.; In Southern Togo, maize grain yield was very responsive to fertilizer N rate in both growing seasons. Splitting fertilization into two applications of equal amount, at two weeks after planting and at the V10–V12 stage, was the appropriate N management technique. The economic optimum N rate was 125 kg N ha-1 for the first growing season, and rates below 90 kg N ha-1 are not recommended as they can result in lost profit. Maize production in the second growing season is subject to uncertainty because of rainfall shortage. Nitrate leaching losses per se and resulting groundwater nitrate levels were very low, indicating that the environmental impact of N use on maize may not currently be of concern in Southern Togo. Application of N rates of 60 kg ha-1 and higher resulted in a net gain of N in both growing seasons. Substituting maize by less N and rainfall demanding crops such as peanut and bean during the second growing season may be an alternative that may allow for optimization of N gained from the first growing season grown to maize, eliminate the drawback of rainfall shortage on farmer activities, and contribute protein to the diet of resource-poor populations. LEACHMN was evaluated for conditions in Southern Togo using field-measured soil hydraulic and chemical properties for the model input data, and calibrating the model for N transformation rates. This resulted in accurate predictions of water and N dynamics in the soil. Nevertheless, a more sophisticated mechanism for plant N uptake simulation is needed to increase model accuracy.