An Evaluation of Sulfur‐coated Urea as a Preplant Total Season Nitrogen Supply for Trellised Tomatoes

The use of a controlled release N source for the production of trellised tomatoes ( Lycopersicon esculentum ) which require frequent topdressings would be desirable. Three sulfur‐coated urea (SCU) materials having release rates of 11.4, 21.5, and 29.3% over a 7‐day period were compared to NH 4 NO 3 applied preplant or as multiple applications. Nitrogen rates were 392, 560, and 729 kg N/ha. Marketable yields from an application of SCU 11.4 at 392 or 560 kg N/ha were greater than with the same rate of N as NH 4 NO 3 either as preplant or split applications. When SCU 21.5 or SCU 29.3 was used, the yields were comparable to a single application of NH 4 NO 3 . Differences in fruit number per plot were not significantly related to treatments. However, there was a significant difference in average fruit weight which was correlated with total yield. Tissue N content was highest at the first sampling from a single application of NH 4 NO 3 and lowest from SCU 11.4 . However, at later sampling periods the N content was maintained at a higher level with SCU 11.4 . Although 729 kg N/ha as a single application of NH 4 NO 3 detrimentally affected plant growth and production, this effect was not noted with the sulfur‐coated urea materials.