Forages and pasture management - Sequential grazing of cool- and warm-season pastures

Pasture productivity in Iowa is often limited by low productivity of cool-season grasses during summer. Our overall objectives were to (i) evaluate the impact of legumes on the productivity and nutritive value of cool-season pastures, (ii) evaluate warm-season grasses for summer grazing, and (iii) determine the effects of pasture sequence on the productivity of season-long grazing systems. Cool-season pastures consisted of smooth bromegrass (Bromus inermis Leyss.) alone or in mixture with birdsfoot trefoil (Lotus corniculatus L.), alfalfa (Medicago sativa L.), or kura clover (Trifolium ambiguum M. Bieb.). Warm-season pastures were monocultures of big bluestem (Andropogon gerardii Vitman) or switchgrass (Panicum virgatum L.). Kura clover was the only legume that persisted well over time, and because of this, pastures interseeded with kura clover maintained a higher nutritive value than either those interseeded with alfalfa or birdsfoot trefoil. This resulted in higher total liveweight gains for cattle grazing sequences that included pastures interseeded with kura clover. In general, rotating cattle to warm-season grass pastures during summer was less advantageous than having them remain on cool-season pastures at a lower stocking rate because warm-season pasture nutritive value was lower and declined more rapidly. However, despite lower nutritive value and consequently animal performance, sequences with warm-season grass pastures did perform well under some conditions and may be a desirable alternative under some circumstances. Having a warm-season grass pasture in the grazing sequence provides an opportunity to relieve cool-season pastures when growth conditions become limiting and introduces flexibility into the management system.