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Spotted Response of Overseeded Ryegrass to Sulfur-Coated Urea¹

Sulfur-coated urea (SCU) shows excellent potential as a controlled-release N source for turfgrasses, but highly spotted appearance has always resulted during 3 years of tests in which SCU was used as an early application on winter ryegrass (Lolium perenne L.) overseeded on verticut bermudagrass (Cynodan sp.). Darker green spots 5 to 15 cm in diam constituted 20 to 50% of the surface area, with lighter green grass between the spots. The spots became smaller and the contrast greater as the season progressed. Chlorphyll content determined by methanol extraction of fresh grass was 8.5 mg/g on dry grass basis in representative darker green spots vs. 6.6 mg/g for lighter green interspot areas. Apparently, in the absence of retentive thatch, the large round SCU pellets were readily moved by sprinkler irrigation and rainfall, and concentrated into zones of stability. Poor initial distribution and mower pickup were not determining factors. Where effective thatch is lacking some means of incorporation sufficient to anchor the pellets should be devised.

Key Words: Chlorophyl content • SCU migration

² Professor, Soil Science Dep.

Received for publication March 31, 1975.