Mechanical renovation of shortgrass prairie for increased herbage production.

A study to determine the effects of single ripping, double ripping, and contour furrowing treatments was conducted on shortgrass rangeland in southeastern Wyoming from 1979-1982. The mechanical treatments changed species composition and increased total forage production over the control. Western wheatgrass (Agropyron smithii Rydb.) exhibited increased production on the treated areas compared to the control. Blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Griffiths] production was significantly lower on the double ripping (1981 and 1982) and the contour furrow (1981) treatments than on the control. Needle-and-thread (Stipa comata Trin. & Rupr.) exhibited an increasing trend on the single and double ripping treatment over the control treatment all 4 years. Forbs also showed his trend in 1979, 1980 and 1981 on all renovation treatments, however little difference in forb production was evident in 1982. Total production differences were the greatest in the first year of renovation (1979) and in 1980 when the annual precipitation was below the long-term average. Increased livestock carrying capacities would result in payback of the renovation costs in 4 years. Numerous mechanical treatments have been used on rangeland during the past 40 years to increase herbage production on some range sites. The most commonly used mechanical treatments in the Great Plains are pitting, furrowing, and ripping. Ripping and contour furrowing can increase productivity by disturbing the native sod and shifting the botanical composition to more productive cool-season species (Branson et al. 1966, Rauzi 1975). Success of the mechanical treatments has varied depending on the degree of surface modification. Barnes (1948) found that more than 1.5 m spacing of furrows for interseeding did not significantly improve forage production. However, Barnes (1952) and Rauzi (1968) noted that spacing furrows no more than 0.6 m apart and about 10 to 20 cm deep was the most effective and profitable furrowing treatment. Rauzi (1975) stated moldboard-plow, disc plow, and rotovator treatments increased western wheatgrass (Agropyron smithii Rydb.) by pruning and redistributing the western wheatgrass rhizomes. To be effective on shortgrass rangeland a treatment should increase water infiltration and storage and reduce competition from unwanted vegetation to allow more desirable cool-season species to become established. Branson et al. (1966) found that the 2 most effective mechanical treatments in increasing forage production and water storage were contour furrowing at intervals of 0.9 to 1.5 m and depths of 20 to 25 cm, and broadbase furrowing, which consisted of low dikes about 0.5 m in height. They concluded that effective mechanical treatments modify the soil surface, not the subsoil, to increase retention and storage of precipitation. Wight and Siddoway (1972) and Neff and Wight (1977) found surface modification affects the amount of water available to the plants by preventing runoff, trapping snow, and reducing the number of plants competing for water. The effectiveness of a Authors are agricultural research technican, soil scientist, soil scientist (retired), USDA-ARS, High Plains Grasslands Research Station, 8408 Hildreth Road, Cheyenne, Wyo. 82009, respectively; and area range conservationist, Soil Conservation Service, Torrington, Wyo. 82240. Acknowledgement is given to D. Heyne, district conservationist, Soil Conscrvation Service, Cheyenne, Wyo., for his assistance in obtaining landowner cooperation and development of the project. Manuscript accepted May 3, 1984. specific surface treatment was dependent on range site and vegetation characteristics. Mechanical disturbances of native sod have also resulted in the release of plant nutrients through soil weathering and decomposition of organic matter (Wight and White 1974). They found that western wheatgrass quickly reinvaded disturbed areas and significantly increased total forage production. Changes in species composition resulting from surface modification can be relatively permanent. Wight and Siddoway (1972) noted that abandoned cultivated fields of the Northern Plains became dominated by needle-andthread (Stipa comata Trin. & Rupr.) and western wheatgrass, resulting in higher production than the contiguous undisturbed range. Estimations of surface modification longevity range from 15 to 25 years. Rauzi (1974) estimated longevity of range pitting in southeastern Wyoming to be about 15 years, depending on range site, climate, and management. Fisser et al. (1974) stated production on contour furrows would probably remain higher than the untreated native rangeland for at least 20 years. Wight and White ( 1974) estimated longevity of lister furrows and pits to be 15 and 25 years, respectively. The purpose of this study was to determine the effects of contour furrowing and ripping of shortgrass rangeland on herbage yields, botanical composition, and livestock carrying capacity.