Tiller dynamics and nutrient content of little bluestem (Schizachyrium scoparium) under ungrazed and heavily grazed conditions

Abstract

The tiller dynamics and nutrient contents of little bluestem (Schizachyrium scoparium) were investigated near College Station, Texas. The objectives of this study were: (1) to determine the rate of growth senescence, and disappearance of little bluestem leaf blade in an ungrazed pasture; (2) to determine the rate of growth, senescence, and disappearance of little bluestem leaf blade under heavy stocked short-duration grazing system; (3) to determine the frequency and intensity of defoliation of little bluestem under heavy stocked short-duration grazing system; and (4) to determine the effects of seasons and stocking rates on crude protein (CP) and in vitro digestible organic matter (IVDOM) of live and dead, leaf and stem fractions of little bluestem before and after grazing in a short-duration grazing system. The use of non-destructive sampling in determining net aboveground productivity (P(,n)) using green leaf blade area growth rate as a parameter of productivity was feasible. The techniques were simple and direct and allowed calculations of senescence and disappearance rates of live and dead leaf materials through direct measurements of net aboveground productivity (P(,n)) and standing green and dead leaf blade areas. There were distinct patterns in the ungrazed and grazed pastures for relative leaf blade area growth rate, senescence rate, and disappearance rate. Growth rates in the grazed pastures were comparable to the ungrazed site. However, senescence and disappearance rates were lower on the grazed pastures. This resulted from consumption of standing green and dead leaves. Efficient forage harvest by grazing was evident on the grazed pastures. The high proportions of tillers grazed and the severity of defoliation were the result of a very heavy stocking rate despite short grazing periods. Pasture utilization was very high. Heavy stocking rates combined with dry conditions resulted in slow regrowth and recovery of the pastures. A high stocking density can be used provided the grazing periods are short enough to prevent excessive defoliation and the rest periods are long enough to allow for pasture regrowth and recovery...