NITROGEN FERTILIZATION FOR MAIZE BASED ON ATTAINABLE YIELD AND SOIL ORGANIC MATTER CONTENT

Agricultural soils generally do not provide enough N to satisfy crop needs, so it is necessary to apply it as fertilizer. This supply can be estimated by chemical analysis of the soil and, based on this and the needs of the plant, nitrogen fertilization recommendations are made for the crops. The objective of this study was to determine economic optimum N rates for maize (Zea mays L.), based on attainable yield and soil organic matter content as an estimator of soil N supply, with the current and increased N/maize price ratio, to reduce economic optimum N rates and fertilization costs, as well as N losses and environmental pollution. In 2011, 2012, and 2013, 67 experiments on maize response to N were distributed and conducted in five edaphoclimatic regions of Mexico, with native and improved maize in rainfed and irrigation conditions. The treatments were: (1) fertilization with N, P, and K; (2) omission of each nutrient; and (3) no fertilization. The experimental design was a randomized complete block design, without replications. Production functions were estimated for rainfed and irrigation conditions in edaphoclimatic regions, for yield as a function of attainable yield classes, amount of N applied, and soil organic matter content. The production functions were used to estimate economic optimum N rates, with: (1) the current N/maiz price ratio for the attainable yield classes and soil organic matter contents, as well as economic optimum yields and net income, for rainfed and irrigated conditions, in the edaphoclimatic regions; and (2) the increased N/maize price ratio, that reduced the economic optimum N rates and fertilization costs, without significantly decrease of the economic optimum yields and the net income; this also reduces N losses and environmental pollution.