Sulfur‐Coated Urea for Turfgrass Fertilization

Abstract

AbstractThe acceptance of sulfur‐coated urea (SCU) as a fertilizer in the turfgrass industry requires a firm basis on which to make recommendations for its use. Three SCU materials were evaluated at different rates and timing of application for maintenance fertilization of ‘Merion’ Kentucky bluegrass (Poa pratensis L.). Two were SCU materials from the Tennessee Valley Authority (TVA): SCU‐11 and SCU‐25, having 11 and 25% 7‐d dissolution rates, respectively. The third, CIL‐30 (30% dissolution rate), was SCU prill from Canadian Industries Limited (CIL). Ammonium nitrate (AN), ureaform (UF), and isobutylidene diurea (IBDU) were also evaluated for comparison with SCU. Response to fertilization was measured by weekly determinations of clipping yields and color. Nitrogen recovery in the clippings and residual SCU pellets in the turf stand were also determined. Data were collected for three growing seasons.The most uniform turfgrass response to SCU fertilization was produced by split applications of 245 kg N ha−1 y−1; and response to SCU‐11 was less than that to SCU‐25 and CIL‐30. When SCU‐25 and CIL‐30 were applied at a rate of 245 kg N/ha in single fall applications, there was insufficient carry‐over of residual N to maintain dark color throughout the growing season. During the first 2 y, release of N from SCU‐11 tended to be too slow to maintain good season‐long color, with only the single spring application of 245 kg N/ha maintaining good color throughout the summer. Response improved in the third year. Fertilization rates of 147 kg N ha−1 y−1 did not produce acceptable quality turf.Pellet recovery from the turf was inversely related to N recovery in plant tissue. Two months after application, SCU dissolution ranged from 91 to 97% for CIL‐30, 60 to 80% for SCU‐25, and 38 to 53% for SCU‐11. Recovery of applied N in the clippings was highest for AN and CIL‐30 with 49 to 59% and 50 to 56% recovery, respectively. Nitrogen recoveries of 42 to 52% and 25 to 37% were obtained for SCU‐25 and SCU‐11, respectively. Recovery was 22% for UF and 46% for IBDU. Response to IBDU compared favorably to SCU‐25, while response to UF was less than from any other 245‐kg split treatment.