As new nitrogen (N) sources are introduced, it is important that they be evaluated and their release characteristics determined in order to provide us with a basis on which to make fertilizer recommendations. In this study, several N sources were evaluated for maintenance fertilization of Kentucky bluegrass (Poa pratensis L.) turf. Treatments included isobutylidene diurea (IBDU) materials of two particle‐size ranges, sulfur‐coated ureas (SCU) in two size ranges from Canadian Industries Limited (CIL), SCU from the Tennessee Valley Authority (TVA), ureaformaldehyde (UF), activated sewage sludges, Organiform, soluble N sources, and combinations of slow‐release and soluble N. All N sources were applied at a rate of 197 kg N·ha−1·yr−1, divided into equal fall and spring applications for 3 consecutive years. Weekly clipping yields, color ratings, and annual N recovery were the response criteria.Sulfur‐coated urea produced a more uniform growth and had higher N recovery than IBDU, which was characterized by a delayed response following fertilization. Turfgrass response to the CIL and TVA SCU materials applied alone was similar. Particle‐size effects with CIL SCU were slight; however, N release was quicker from fine IBDU than coarse IBDU. Slow‐release characteristics were also observed for ureaform, Organiform, and the sludges, but turf quality was generally poor for these treatments. Substituting soluble N for a portion of the SCU N gave inferior turfgrass response as compared to SCU applied alone. When soluble N was used in conjunction with ureaform, Organiform LT, and IBDU, turfgrass response was improved over that obtained when these N sources were used alone. Recovery of N in the clippings was greatest for soluble N sources and SCU treatments (48 to 52%), while lowest values (15 to 29%) were associated with ureaform, Organiform, and sludges.
New resin coatings have been developed for producing slow‐release fertilizers for turfgrasses. It is important that new fertilizer materials be evaluated so that recommendations can be made for their use. Four experimental resin‐coated ureas (RCU) were evaluated for maintenance fertilization of Merion Kentucky bluegrass (Poa pratensis L.) turf grown on an Arkport sandy loam (coarse‐loamy, mixed, mesic Psammentic Hapludalfs). The RCUs had an analysis of 41% N and laboratory release rates of 270 d (RCU‐270), 100 d (RCU‐100), and 70 d (RCU‐70). A mixture of the RCU materials (RCU‐M), sulfur‐coated urea (SCU), urea, a 22–1.8–6.6 with 10% by weight dicyandiamide (DCD), and oxamide were included for comparison. The fertilizers were applied at an annual rate of 196 kg N ha−1, as single‐spring or split‐spring, and fall applications. The most rapid response to fertilization as measured by fresh weight yields and color ratings was produced by urea, followed in order by SCU, RCU‐70, and RCU‐100. The release rate of RCU‐270 was too slow to produce acceptable color ratings through much of the test at both fertilization times. The most uniform response was produced by RCU‐100 at both the single‐spring and split treatments. The highest N recovery in the leaf tissue was obtained from oxamide (24 and 59%), the single‐spring application of SCU (27 and 58%), and the split applications of RCU‐100 (21 and 52%) and RCU‐70 (25 and 54%). Nitrogen recovery from SCU was highest in growth periods immediately following fertilization, while recovery was more uniform across growth periods with the RCU‐100. Certain RCU fertilizers are well suited for turfgrass fertilization.
The 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.
As new herbicides are investigated for use on turf, it is important to study the effects continued use of these materials have on desirable grass species. A field investigation was conducted to determine the influence of prodiamine [2,4‐dinitro‐N3,N3‐dipropyl‐6‐(trifluoromethyl)‐1.3‐benzenediamine] application rate and frequency on Kentucky bluegrass (Poa pratensis L.) turf over a 4‐yr period. Root mass and turfgrass density decreased following prodiamine treatment. Turfgrass quality ratings decreased as prodiamine rate increased, but remained acceptable at rates below 1.1 kg ha−1 a.i. The projected use rate for prodiamine in the northeastern USA is 0.56 kg ha−1 a.i. Quality was reduced and necrotic ring spot (Leptosphaeria korrae Walker and Smith) disease more severe when prodiamine was applied annually vs. biennially. Percent turf area damaged by necrotic ring spot also increased as prodiamine rate increased, but was most severe at rates greater than 2.2 kg ha−1 a.i. The quality, density, and disease data indicated that annual applications of prodiamine can be detrimental to Kentucky bluegrass turf. These results suggest that it may be advantageous to avoid prodiamine applications in successive years or to alternate it with less phytotoxic preemergence herbicides.
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