Nitrogen and phosphorus are the main soil fertility constraints for improving crop production on hillsides of Honduras and Nicaragua. In 2004, members of the Integrated Management of steep land soils (MIS) Consortium and researchers from the Soil Management CRSP-USAID, initiated 2-year trials at eight locations in Honduras and Nicaragua to acquire corn cultivar and soil coefficients for developing improved nitrogen fertilizer recommendations using Nutrient Management Support System (NuMaSS) software (Osmond et al., 2004). The amount of nitrogen fertilizer recommended is the balance between the total amount of nitrogen needed by the crops and nitrogen acquired from the soil, plant residues, and cover crops, with adjustment for nitrogen fertilizer use efficiency by the crop. Although the software provides default values derived from reviews of existing publications for many of these plant factors, it is possible to generate specific nitrogen fertilizer recommendations for prevailing cultivars and soils cropped in the region. Eleven on-farm plot experiments were established using seven urea-N rates (0, 20, 40, 80, 120, 160 or 200 kg N ha^-1). At each trial site, data were collected for nutrient content of soils and plants, and stover and grain yield. The yield response curve at one of the field sites showed an increase with application of nitrogen fertilizer at a maximum rate of 7.4 t ha^-1. The quantity of nitrogen required to reach this yield was 106 kg N ha^-1. The quantity of total nitrogen uptake by the crop was estimated by NuMaSS to achieve this yield, using a default grain:stover ratio value of 128 kg ha^-1. When the experimental grain:stover value (1.11) was used, NuMaSS estimated total crop nitrogen uptake as 116 kg ha^-1, less nitrogen than the default software value. Data regarding nitrogen content of grain and stover, native soil nitrogen content, and nitrogen fertilizer recovery for a specific cultivar and soil can be applied to NuMaSS to improve local nitrogen application recommendations. There was a 2.5-fold difference in grain:stover ratios among the predominant corn cultivars cropped in Honduras and Nicaragua. Maximum yields from the six trial sites differed by over 5 t ha^-1 and optimum nitrogen fertilizer rates ranged from 0 to 113 kg ha^-1. These differences in cultivar characteristics and differences in yield potential and native soil nitrogen supply among the trial sites indicate that improved nitrogen fertilizer recommendations require knowledge of both the intended crop cultivar and site characteristics.