Urea-Ammonium Sulfate and Urea-Ammonium Phosphate Evaluation as Nitrogen Sources in the Southeast

Recent increases in N fertilizer cost emphasize the need for information concerning the use of cheaper N sources to produce the most marketable yield per unit fertilizer cost. Urea-ammonium sulfate (UAS) and urea-ammonium phosphate (UAP) are two new fertilizer products in which urea is the main source of N. These materials were compared to ammonium nitrate (AN) as N sources for corn (Zea mays L., Coastal bermudagrass (Cynodon dactylin L. Pers.), and rye (Secale cereale L.). Each material was used to supply N at rates from 0 up to 448, 336, and 135 kg/ha on Coastal bermudagrass, corn, and rye, respectively. All crops were grown on Tifton soil (Plinthitic Paleudult; fine, loamy, siliceous, thermic). Corn was also grown on a Greenville soil (Rhodic Paleudult; clayey, kaolinitic, thermic). Recommended cultural practices normally used in the area were followed for each crop. Forage yield for Coastal bermudagrass and rye was measured and selected samples analyzed for ammoniacal N concentration. Corn grain yield was measured. Selected soil samples from the corn experiment were analyzed for nitrate-N. Percent N increased in Coastal bermudagrass and rye forage as N application rate increased. Coastal bermudagrass recovered less N from both UAP and UAS than from AN at the 336 kg/ha N rate. All materials were equivalent as N sources for rye and corn. Irrigation of the corn was found to increase yields as well as nitrate-N leaching. Applying 50% of the 336 kg/ha N at planting and the rest later to prevent leaching in corn production was no better on Tifton and Greenville soils than a single preplant N application of either 168 or 336 kg/ha. For Southeastern Coastal Plain conditions the two fertilizers evaluated could replace AN in corn and rye production without loss in N concentration, yield, or N use efficiency. The materials tended to be less efficient than AN in supplying N for Coastal bermudagrass production.