This study was initiated in Oregon in 1980 to monitor the effects on forage production of simultaneously varying both defoliation frequency and defoliation intensity in a grass-clover (Lolium perenne-Trifolium subterraneum) pasture. Dry matter yield was directly related to defoliation interval. The relationship between dry matter yield and defoliation interval was generally a power curve with yield increasing rapidly as the period between defoliation events increased from 1-49 days. The erect-growing perennial ryegrass-dominated sward in 1980 had its highest yield under high stubble heights. The more prostrate subclover-dominated pasture of 1982 yielded more when defoliated closer to the ground. It appears that dry matter is more sensitive to the interval between defoliation than it is to severity of defoliation. This was true for defoliation intervals greater than 3 weeks. These data suggest that the short-duration grazing practice of increasing the interval between grazings, even if it is achieved at a cost of increased severity of each defoliation event, is compatible with high forage production.
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