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

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Abstract
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.