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The central temperate Argentinean region is currently affected by rising water tables, allowing higher and more stable maize yields (Zea mays L) when they fluctuate within optimum depth. However, limited information was available for optimizing N management in these environments. Yield response to N rates was explored in soils with influencing groundwater (always <3.5 m depth), and different environment and management variables were examined to help explain differential yield responses across sites. A total of 15 rainfed experiments (site × year combinations) were conducted with five N rates (0-240 kg N ha −1) tested at two different timings (sowing and V7) in a factorial design. A consistent yield response to N rate was evident, increasing yields from 2,300 to 6,900 kg ha −1 across sites. Yields at maximum N levels ranged from 13,700 to 16,900 kg ha −1. Fertilization timing had a minor and inconsistent effect on yield across sites. At a maize grain/fertilizer N price ratio of 10, the economically optimal N rate ranged from 117 to 206 kg N ha −1. Soil N-NO 3 at sowing, previous crop, and apparent-indigenous N supply (INS) helped explain differential yield responses across sites, and response models for obtaining economic optimum rates considering the influence of these variables are provided. These results highlight the relevance of N rate, rather than timing, as a critical crop management decision in environments with high water availability and yield.

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