How Much Forage Should be Ungrazed and How Much Can be Eaten? Certain amounts of plant residue (ungrazed herbage) must be maintained to protect the soil, ensure rainfall infiltration and sustain forage production. Ungrazed herbage is an investment in future forage production. The minimum residue levels needed to sustain production are 300 to 500, 750 to 1,000 and 1,200 to 1,500 pounds per acre (oven dry weight) of shortgrasses, midgrasses and tallgrasses, respectively. Figure 5 shows the proper residue level (1,500 pounds per acre) for a tallgrass prairie site near Bowie, Texas. When forage is reduced below threshold levels, rainfall doesn't infiltrate the soil as deeply and animals don't perform as well. But when proper amounts of forage are left ungrazed, rainfall infiltrates the soil and preferred plant species become better established and produce more forage than if grazed too closely. In one study in south Texas, when grazing pressure reduced forage supplies below about 750 pounds per acre, cattle consumed more browse and their intake of organic matter, digestible energy and crude protein rapidly declined (Hanson and Stuth, 1988). In a similar study in the eastern Rolling Plains of Texas, organic matter intake declined when forage supply was below 623 pounds per acre (Pinchak, et al., 1990). In both studies animal performance declined when forage supplies fell below these threshold levels. The principle governing stocking rate decisions is to "take half and leave half." This means that of the total forage produced during the year, half should remain ungrazed. Of the half that is available for livestock consumption, half of that amount (25 percent of the total forage production) will generally be lost to insects, weathering, trampling, other animals and decomposition. Thus, when properly stocked, rangeland will achieve about a 25 percent harvest efficiency (25 percent actually consumed by livestock). Authors: Larry D. White, Allan McGinty