Effects of Clipping on Burned and Unburned Creeping Bluestem

Abstract

Creeping bluestem (Schizachyrium stoloniferum), a major decreaser on Florida range, is adversely affected by grazing during the growing season after a winter burn. To compare the effect of defoliation of burned and unburned bluestem range, creeping bluestem was burned (or not burned) on 2 similar sites in February 1978 and 1979 and cut at 2, 4, 6, 8, and 10 months after burning. Once forage was initially cut, it was recut every 2 months. Dry matter (DM) yield, tiller density, total nonstructural carbohydrate (TNC), crude protein (CP), and in vitro organic matter digestibility (IVOMD) were determined. When forage was cut in April and recut every 2 months, average yield of creeping bluestem from unburned areas was 3,000 kg/ha while that of burned was 2,350 kg/ha. Creeping bluestem yield from unburned areas declined linearly within both years as initial harvest was delayed, but delaying initial harvest date had no effect on forage yield from burned areas. Final tiller density was usually a cubic response in burned and unburned plants. Tiller density generally increased in plants cut 1 month after treatment, decreased in plants cut 2, 4, 6 months after treatment, and increased in plants cut 10 and 12 months after treatment. Rhizomes of plants burned in February 1979, cut initially in April, and reharvested 4 times had 9.0% TNC in March 1980, while unburned plants contained 10.2% TNC. The response of CP and IVOMD in initial growth was quadratic or cubic with time of initial harvest because percentages were raised initially due to burning, then they dropped steadily to a low in August, after which they began to rise slightly. Protein content in unburned forage had either a negative linear response or had no significant regression with time of initial harvest. IVOMD in unburned forage exhibited a quadratic (1978) or a polynomial (1979) response with time of initial harvest where IVOMD increased or fluctuated in the growing season, usually decreasing in fall and winter. Analysis of regrowth data indicated that the response of crude protein and IVOMD was similar regardless of burn treatment. Quality of regrowth declined from June to August and steadily increased from August to December. Creeping bluestem would be weakened by grazing on 60-day intervals after a February burn. When prescribed burning of creeping bluestem range is carried out every 3 to 4 years, deferment of grazing until June after a February burn will allow grazing of relatively high quality forage and still maintain creeping bluestem stand vigor.