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Evaluation of Oxamide as a Slow-Release Nitrogen Source on Kentucky Bluegrass¹

Slow-release N fertilizers are used in turfgrass fertilization programs to reduce foliar burn and N losses, and to extend the response period between applications. In this study, oxamide (31% N), an amide of oxalic acid, and a 7:3 N ratio of oxamide and urea were evaluated as slow release N sources on Kentucky bluegrass (Poa pratensis L.) at West Lafayette, IN, on a Toronto silt loam soil (fine-silty, mixed mesic, Udollic Ochraqualfs). Two particle sizes of oxamide, C (1-2.8 mm) and F (<0.85 mm), were applied as a granular and liquid suspension treatment, respectively. Additional treatments consisted of applying isobutylidene diurea (IBDU), sulfur-coated urea (SCU), and urea. Two and four applications were made, with a total annual application rate of 196 kg N ha^–1 yr^–1. Recovery of N in the tissue from applications of oxamide C was 51% compared to 41, 39, and 38% for IBDU, oxamide F, and SCU, respectively, averaged over 3 yr. Initial change in visual turf quality and clipping yields in response to oxamide C was slow, similar to that of IBDU; however, residual N release was equal to that of IBDU and greater than that of SCU. Adding urea to oxamide C increased initial yields and turf quality but reduced the duration of turf response as compared to applications of oxamide C alone. At two applications of 98 kg N ha^–1, oxamide proved to be a good, slow-release source of N. At four applications per year, initial clipping yields resulting from spring oxamide F applications were lower than those from urea, but turf quality in response to residual N tended to be greater than that of urea. Late fall applications of oxamide F reduced soil NO^–₃ concentrations shortly after application and in early spring as compared to fall applications of urea. Oxamide F at four applications generally produced a more desirable turf response than did similar applications of urea.

Key Words: Isobutylidene diurea • Sulfur-coated urea • Nitrogen recovery • Soil inorganic nitrogen • Poa pratensis L.

² Former research assistant (current address: O.M. Scott, Research, Marysville, OH 43041), professor of agronomy, and professional scientist, Purdue University, W. Lafayette, IN.

Received for publication February 10, 1986.