SULFUR FERTILIZATION OF SMOOTH BROMEGRASS IN KANSAS

Sulfur deficiencies have been identified throughout the central USA with increasing frequency in recent years, yet little work has been reported on S needs of perennial cool-season forage grasses. Field studies were initiated on established smooth bromegrass (Bromus inermis Leyss.) at three sites in eastern Kansas to evaluate the effects of S fertilization on forage production and quality. Sulfur rates (0, 17, 34 kg ha(-1)) and sources (ammonium sulfate and ammonium thiosulfate) were evaluated with a uniform N application of 134 kg ha(-1). Sulfur fertilization generally increased bromegrass forage production. Averaged across site-years, forage yields were increased 700 kg ha(-1) annually by S application. The 17 kg S ha(-1) rate was sufficient to achieve forage yield increases. Sulfur fertilization had little effect on bromegrass forage protein levels at normal harvest time, but did increase forage S concentrations. Forage protein levels of early-season forage samples were increased by S application. When N/S ratios of the no-S check treatments were 20:1 or greater, forage yields were increased with S application. Ammonium sulfate and ammonium thiosulfate performed equally well as S sources.