Evaluation of Sulfur‐coated Urea Fertilizers on Merion Kentucky Bluegrass

Abstract

AbstractSulfur‐coated urea (SCU) appears to be both agronomically and economically feasible for use as a slow‐release N source on turfgrasses. Because considerable variation can occur among SCU products, this study was conducted to evaluate six formulations that were representative of different coating weights and coating methods.Five experimental formulations from the Tennessee Valley Authority and Gold‐N, a product of Imperial Chemical Industries, were applied to ‘Merion’ Kentucky bluegrass (Poa pratensis L.) at a rate of 195 kg N/ha in the spring of 1974, 1975, and 1976. Coating weights of S on TVA materials had been varied to obtain laboratory 7‐day dissolution rates of 17, 26, and 35% from material coated with S only; and 16 and 26% from material coated with S plus a wax sealant. Gold‐N was coated with S plus a paraffin sealant and had a dissolution rate of 36%.Clipping weights and turf color were used to evaluate turfgrass response. With S‐only coatings, turfgrass response increased as coating weight decreased (dissolution rate increased). Differences due to coating weight were greatest in the first year, and diminished in the following years. In yield and color comparisons over three seasons, a low dissolution rate treatment never produced more response than a higher dissolution rate treatment. In comparison of materials with similar dissolution rates but with different coating methods, release of N was more rapid with a S plus wax coating than with a S‐only coating. The 7‐day dissolution rate was not dependable in predicting field response when coating method was varied.Plots were sampled for residual CSU in 1976, 1977, and 1978. After three growing season, residual SCU pellets ranged from 3 to 37% of the total applied weight; and after 2 additional years in which no fertilizer was applied, 0 to 13% remained. Variations in SCU formulation caused significant differences in turfgrass response to fertilization and in the amount of residual material; thus, factors such as coating weight and method should be known and taken into consideration when developing a fertilization program based on SCU.