The objectives of this paper is to compare in situ availability of nitrogen and phosphorus content at two field sites. One site received three annual additions of manure from swine fed low-phytate corn or traditional corn diets or inorganic fertilizer, surface applied to rainfed no-till sorghum [Sorghum bicolor (L.) Moench]. A second site received a one-time application and incorporation of the same nutrient treatments to irrigated corn. Potentially mineralizable N was 70% of applied N and extractable P was 100% of applied P for manure from both diets. Incorporation of swine slurry reduced potentially mineralizable N to 40% the year of application and 30% the year after application and reduced extractable P to 60% the year of application and 40% the year after application for both diets. Modified diets reduced the P content of the manure but not the availability of N or P.