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Gaseous Ammonia Losses from Urea Solutions Applied as a Foliar Spray to Various Grass Sods¹

ABSTRACT

The gaseous loss of NH₃ from urea applied to plant sods was studied under laboratory conditions, using various grasses which had been grown in pots under greenhouse conditions. Spray applications of N¹⁵- and C¹⁴-labeled urea solutions equivalent to 50, 100, and 150 pounds of N per acre were made to the potted plant samples which had been transferred to a bell-jar apparatus. Care was taken to spray as much of the solution as possible directly on the plant foliage. The total amount of NH₃ lost through volatilization, as measured over a period of 8 to 10 days, increased with increasing rates of application. Losses ranged from about 0.5 pounds per acre with a 50-pound application to about 45 pounds with the 150-pound application. A lag period of 2 to 3 days occurred before any measurable quantity of NH₃ was lost from any of the plants, with the exception of bluegrass. The greatest amount of urea hydrolysis, as measured by C¹⁴O₂ evolution, occurred during this 2- to 3-day period. The amount of NH₃ lost and the rate of urea hydrolysis were influenced somewhat by the type of sod to which urea was applied. In most cases, there apparently was little or no direct relationship between C¹⁴O₂ evolution and the NH₃ lost.

¹ Contribution from the Department of Agronomy, University of Illinois, Urbana. Published with the approval of the Director of the Illinois Agr. Exp. Sta. Presented before Div. IV, Soil Science Society of America, Chicago, Ill. Dec. 5, 1960. The investigation was supported in part by a research grant from the American Farm Research Association. The results of the experiments were used by the senior author in 1961 in partial fulfillment of the requirements for the Ph.D. degree from the University of Illinois.

² Former Research Assistant in Soil Fertility, present address Simpson Fertilizer Co., Red Bud, Ill., and Professor of Soil Chemistry, respectively.