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Evaluation of Urea-Urea Phosphate as a Nitrogen Source for No-tillage Production¹

ABSTRACT

Urea-urea phosphate (UUP), a combination of urea and phosphoric acid, has properties which reduce the potential for NH₃ volatilization but has not been evaluated extensively under field conditions. The objective of this study was to evaluate UUP (34-17-0) under laboratory and field conditions. All experiments were conducted on acid sandy soils typical of the predominant Ultisols found in the southeastern USA. A forced-draft technique was used to make direct measurements of NH₃ losses in a growth chamber and also in the field. In addition, UUP and six other N sources were compared for no-till grain sorghum (Sorghum bicolor L. Moench) production. Direct measurement of NH₃ losses in the growth chamber resulted in small losses from UUP on both mulched and bare soils, while NH₃ losses from urea ranged from 15 to 32% of the applied N on a bare soil and 68 to 82% on a mulched soil. Direct field measurement of NH₃ losses from urea, UUP, and ammonium nitrate applied at 200 kg N/ha were 19, 5, and 2% of the applied N, respectively. In the field plot studies, UUP compared favorably with ammonium nitrate and calcium nitrate with respect to crop response. The mechanism of NH₃ loss prevention appears to be pH buffering by the phosphoric acid component of UUP. It is concluded that UUP is an effective N source for surface application to noncalcareous soils under no-tillage management.

¹ Contribution from the Dep. of Agronomy, Georgia Agric. Exp. Stn., Experiment, GA 30212-5099, and the National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals, AL 35660. Supported by State and Hatch funds allocated to the Georgia Agric. Expt. Stn. and by funds from TVA.

² Graduate Research Assistant, and Associate Professor, Dep. of Agronomy, Georgia Agric. Exp. Stn.; Research Soil Chemist, Agricultural Research Branch, NFDC-TVA; and Laboratory Research Assistant, Dep. of Agronomy, Georgia Exp. Stn., respectively. Senior author is presently Graduate Research Assistant, Agronomy Dep., Rutgers Univ., New Brunswick, NJ.

Received for publication May 19, 1986.