Phosphorus (P) needs for corn (Zea mays L.) are typically met by applying Mono-Ammonium or Di-Ammonium Phosphate (MAP and DAP). In most of the Midwest, P is commonly applied in the fall before growing corn. The N in the fertilizer is often assumed to be available to the corn; however, research has not confirmed this assumption. Field trials were established in Waseca, MN (Webster cl) and Urbana, IL (Drummer sicl) to determine the availability of N from fall and spring, preplant-applied DAP, MAP, and ammonium sulfate (AMS) to corn during 2004 to 2006. Each N source was applied at 45 and 90 kg N ha^-1. Control and AMS plots received 112 kg P₂O₅ ha^-1. Treatments were arranged in a randomized complete block design. Also, a soil (Cisne sil and Drummer sicl) incubation study was conducted to measure the rates of nitrification and denitrification of MAP and DAP at 80 and 120% field capacity (FC). After 2 weeks of incubation at 80%FC nearly all N had been nitrified for both MAP and DAP. At 120% FC all the nitrate was denitrified by week 8, whereas over 50% recovery was observed at 80% FC after 16 weeks of incubation. In the field, differences among N sources were generally not found for any of the soil N or corn production parameters measured. Nitrification of fall-applied N was completed by the end of April. Efficiency of fall-applied ammoniated phosphate was diminished in wetter than normal springs due to denitrification and immobilization. Mean recovery of total inorganic N for all sites-years at the end of May from the top 30 cm of the soil was 17% for fall- compared to 48% for spring-applied N. Corn yield averaged 554 kg ha^-1 lower for fall applications compared to spring applications.