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Forage quality and quantity and stand vigor of bigsacaton were evaluated for seven defoliation systems during 1977 and 1978. Big sacaton plants were either shredded monthly, shredded in spring /midsummer, spring/early summer, spring, spring/late summer /fall, midsummer/fall, or late winter. Forage quality of big sacaton was improved by defoliation during both years. With few exceptions, crude protein content was highest in plants defoliated the previous month. IVDOM contents were also improved by defoliation. Digestibility decreased to below 50% in early summer in nonshredded plants and in mid summer in all plants regardless of prior defoliation treatment. IVDOM increased to above 50% in late summer and fall in plots defoliated the previous month. Forage harvests during the growing season were greatest from plots that were defoliated three or more times and were defoliated in the fall. The least amounts of forage were harvested from the plots defoliated in spring, spring/early summer and spring/midsummer. In the fall and winter the nonshredded and spring defoliated plots supported relatively large amounts of forage, and the spring/early summer and spring/midsummer plots supported intermediate amounts of forage for winter grazing. Stand vigor was maintained best by brief periods of defoliation in the spring or spring/early summer, followed by defoliation of old forage in late winter. Vigor appeared to be decreased by early fall defoliations to a 7.5 cm stubble height. The spring/early-summer system provided large amounts of high quality forage and maintained stand vigor. This system defoliated plants when soil moisture was usually adequate for plant regrowth, provided nutritious forage during the growing season and provided adequate standing forage for fall and winter grazing and protection against damage due to low temperature. Big sacaton (Sporobolus wrightii Munro) is a robust perennial bunchgrass which occurs from Arizona to western Texas and south into Mexico (USFS 1937). The species grows mainly on low alluvial flats, bottomlands, and arroyos subject to flooding. Big sacaton will not generally grow on soils highly impregnated with alkali (Wooton and Standley 1912). Although it is a warm-season species, it begins growth early in the spring and may remain green throughout mild winters. The author. formerly an assistant professor, Texas Agricultural Experiment Station. (Department of Range Science), Texas A&M University. College Station 77843. Currently is an assistant professor, Eastern Oregon Agr. Res. Center. Squaw Butte. Oregon State University, Box 833. Burns. OR. 97720. This report is approved for publication by the director. Texas Agricultural Expcriment Station. as Tech. Article 15848. The author greatly acknowledges the J.S. Abercrombie Foundation. Houston. Texas. for funding the project; Mr. George T. Jambers. Jr., for providing land and assistance for the study: and the U.S. Dep. Agr. Soil Conservation Service for cooperation inestablishing the planting. The planting was established by Mr. George Jamben. Jr., in cooperation with Mr. Joe Coughran, district conservationist with the U.S. Dep. Agr. Soil Conservation Service stationed at Tilde”, Texas. Plant materials were provided by the Soil Conservation Service Plant Materials Center, Knox City. Texas. The author is grateful to Mr. David Davidson, Mr. Gary Bowers, Dr. James George. and Mr. Keven Van Hook for help with plot installation. maintenancc,and evaluation of the study. I also thank Mr. Ray Hinnant. Mrs. Julie Averit, and MS. Mary Lee Skwirz for their assistance in analyzing samples, and Mr. Don Shelton for assistance in the statistical analysis. Manuscript received March 4. 1980. Early spring growth is readily grazed by animals and big sacaton has been mowed during the growing season for hay (Humphrey 1960). Griffiths et al. (1915) reported big sacaton contained 9.25% crude protein when harvested at flowering to a stubble height of 10 cm. The plants produce a large volume of herbage which cures well and reportedly provide a source of good winter forage despite their coarseness (USFS 1937). However, Humphrey (1960) reported the mature foliage was rarely grazed. Rangemen have long been aware that grazing, mowing, or burning can affect yield and quality of forage (Youngner 1972). The USFS( 1937) reported theabundance of big sacaton had been reduced in many areas by overgrazing, but careful management would apparently allow full use of the species and maintain stands in a productive state. Sacaton flats can be used most effectively by grazing heavily early in the spring and then deferring until fall (Humphrey 1960). The Soil Conservation Service (1979) suggests grazing of big sacaton plants no closer than 20 to 25 cm stubble heights and then resting for 4 to 6 months. Coarse, unpalatable mature growth may be removed by burning every 3 or 4 years with less damage occurring to big sacaton plants burned in late winter or early spring before growth begins (Humphrey 1960). Bock and Bock (1978) reported that burning an ungrazed big sacaton community in the summer and winter in southeastern Arizona reduced the height and cover of big sacaton and stimulated the growth of other grasses and forbs. They found summer fires created more bare ground and encouraged a greater number and variety of annuals than did the winter fire. Previous studies in Texas have shown forage quality of big sacaton to decrease with increasing plant maturity (Haferkampunpublished data). Quality, however, appeared to be maintained at a higher level with frequent defoliations. Specific responses to defoliation appear to vary by plant species due to intensity, frequency, and season of defoliation as associated with climate, soil fertility, and light. Many researchers have reported dry matter production of grasses to be affected by both frequency and height of defoliation (Holscher 1945; Jameson and Huss 1959; Peterson 1962; Auda et al. 1966; Burton et al. 1969). Total dry matter production can be reduced by close or frequent clipping, but digestible dry matter may be increased by an increased frequency of clipping (Burton et al. 1963). Increases in forage quality appear to result from maintaining plants and plant parts in a younger stage of development. This study was designed to investigate the impact of defoliation on forage quality and quantity and stand vigor of established big sacaton, selection “PMT-820”, growing on the South Texas Plains. Materials and Methods Site Description Big sacaton “PMT-820” was drilled in 1968 on 197 cm centers on an Orelia clay loam (Typic Ochraqualfs, Fine-loamy, Mixed, Hyperthermic) soil in McMullen County, Texas. Average annual precipitation for the area is 58 to 61 cm with greatest amounts 26 JOURNAL OF RANGE MANAGEMENT 35(l), January 1982 Table 1. Schedule of defoliation treatments rpplkd in 1977 and 1978 to a big sacaton located in the South Texas Plains near Whitsett. Spring Sample, seasons and dates

Defoliation Impacts on Quality and Quantity of Forage Harvested from Big Sacaton (Sporobolus wrightii Munro)