EFFECTS OF GRAZING MANAGEMENT ON STANDING CROP DYNAMICS IN TALLGRASS PRAIRIE

Grazing system and stocking rate effects on forage standing crop of ta llgrass prairies in north-central Oklahoma were evaluated from 1989 to 1993. Twelve experimental units, consisting of pastures dominated by big bluestem [Andropogon gerardii Vitman], little bluestem [Schizachyr ium scoparium (Michx.) Nash], indiangrass [Sorghastrum nutans (L.) Nas h], and switchgrass [Panicum virgatum L.], were arranged in a complete ly randomized design with either a short duration rotation or continuo us grazing system and stocking rates ranging from 127 kg animal live-w eight/ha to 222 kg live-weight/ha. Yearling steers grazed the units fr om late April to late September. Herbage standing crop was sampled in July and September. Total, live, and dead standing crops did not diffe r significantly between the 2 grazing systems in July. Total standing crop was significantly higher in the rotation units in September (3,60 0 versus 3,020 kg/ha, P<0.05). Dead standing crop was also higher in t he rotation units in September (1,950 versus 1,570 kg/ha, P<0.05). Evi dence suggests the difference in standing crop between systems is due, in part, to reduced forage intake by the livestock. Grazing system di d not interact with either stocking rate or year. Stocking rate had si gnificant effects on total, live and dead standing crops at both sampl e dates. The slope of the total standing crop-stocking rate relationsh ip varied over years and ranged from -12 to -36 kg/ha per kg live-weig ht/ha in July and from -12 to -27 kg/ha per kg live-weight/ha in Septe mber. Higher standing crop at the end of the grazing season in the rot ation units would mean greater soil protection and higher fuel loading for prescribed burning, and would suggest a lower impact on plant vig or. However, if the higher standing crop is a result of lower forage i ntake, we would expect livestock weight gains to decline.