The University of Arizona

Clipping frequency and intensity effects of big bluestem yield, quality, and persistence.

J.R. Forwood, M.M. Magai


This study was initiated to determine the effects of defoliation frequency (based on amount of growth present), intensity, and length of grazing season on quantity and quality of big bluestem (Andropogon gerardi Vitman) in the Southern corn belt and to provide further data regarding the reasons for rapid quality decline of warm-season grasses. Three clipping frequencies (when plants reached heights of 30, 41, 51 cm) at 2 intensities (stubble heights of 10 and 20 cm) were imposed on established plots of pure big bluestem (cv. Kaw). Harvest season length was studied by terminating clipping on 15 August and 15 September as 2 separate treatments. Two years of data indicated that big bluestem regrows insufficiently after 15 August to warrant additional harvests under the imposed managements. Prolonged regrowth and leaving a short stubble of 10 cm resulted in greatest yield. Short stubble led to greater reductions in nonstructural carbohydrates, but did not damage the stand compared to pre-study measurements. Nonstructural carbohydrate levels and stand composition improved with taller stubble. In vitro dry matter digestibility and crude protein were higher on treatments clipped to leave a 10-cm stubble. The greatest proportion of leaves resulted from treatments where a 20-cm stubble remained. These results agree with studies indicating that leaf maturity is more responsible for lower quality forage than is the amount of stem material present in the stand. Our results indicate heavy use can be more safely accomplished in the Southern corn belt than for areas to the west because big bluestem can be more intensively defoliated in the Southern corn belt (10-cm) than that recommended for other areas (20 to 40 cm).


carbohydrates;persistence;Missouri;protein content;cutting frequency;Andropogon gerardii;crude protein;grazing intensity;in vitro digestibility;defoliation;quality;grazing;simulation;forage

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