Establishment of range grasses on various seedbeds at creosotebush [Larrea tridentata] sites in Arizona, U.S.A. and Chihuahua, Mexico.

Perennial grasses were seeded by drilling or broadcasting on 4 mechanical and 3 herbicidal weed control and/or seedbed preparation treatments at 4 semidesert grassland sites invaded by creosotebush (Zarrea tridcnutu) in the Chfuahuan and Sonoran Deserts. The cultivars ‘Cochise’ Atherstone lovegrass (Eragrostis lehmanniana X Eragrostis trichophera) and ‘Catalina’ Boer lovegrass (Effrgrostis curvuIo var. coqferta) lovegrasses were initially established and persisted in 6 of the 8 plantings on disk plowed and disk plowed plus contour furrowed seedbeds. These grasses were established and persisted in 2 of the 5 plantings made in creosotebush stands treated with tebuthiuron [JV-(S-(l,l-dimethylethyl)1,3,4-thiadizol-2-yl)imethylurea] at 0.5, 1.0, and 1.5 kg a.i/ha rates. Grasses established initially on two-way railed and land imprinted areas usually died within 3 or 4 years. Creosotebush (Larrea tridentata), a woody perennial shrub, has invaded the semidesert grasslands within the Chihuahuan and Sonoran Deserts of North America (Humphrey 1958, Buffington and Herbel 1965, Hastings and Turner 1965). As creosotebush densities increase, perennial grass densities decline (Anderson et al. 1957). Therefore, it is desirable to replace creosotebush with perennial grasses to reduce soil erosion, increase infiltration, and provide forage for domestic livestock. Jerry COY. and Howard Morton are range scientist and supervisory plant physiologist, respectively; USDA, Agricultural Research Services Aridland Watershed Management Research Unit, 2000 E. Allen Road, Tucson, Artz. 85719, Martha Martin-R. and Fernando Ibarra-F. are head of the Department of Range Management and Technical Director, respectively, CIPES, Periferico OTS S/N, Conjunto UGRS, Postal 1754, Hermosillo, Sonora, Mexico. When this study was initiated Martha Martin-R. and Fernando Ibarra-F. were graduate students, School of Renewable Natural Resources, University of Arizona, Tucson. Appreciation is extended to Consejo National de Ciencia y Tecnologia (Mexico) for financial support; Elanco Products Company for the herbicide and fencing materials at the Mexican sites; Drs. Luis Carlos Fierro, Thomas N. Johnsen, Jr., and Gilbert L. Jordan for technical assistance; personnel at Rancho Experimental La Campana, Chihuahua, Mexico, and Aridland Watershed Management Research Unit, Tucson, Aria., for setting up plots, applying treatments, and collecting data; and ranchers Eloy Morales, Sergio Mendora, and Gilbert0 Valdez for permission to use their land and housing facilities. The Rocky Mountain Forest and Range Experiment Station gave permission to use land at the Santa Rita Experimental Range. Lovegrass seeds were provided by U.S. Dep. Agr., Soil Conservation Service, Plant Materials Center, Tucson, Arizona. Kleingrass and sideoats grama seeds were provided by Rancho Experimental La Campana. Buffelgrass seeds were provided by Centro de Investigations Pecuarias de1 Estado Sonora, Garbo, Sonora, Mexico. Manuscript accepted 5 May 1986. 540 For the past 90 years creosotebush management has consisted of mechanical tillage to reduce creosotebush competition and prepare a seedbed for seeding perennial grasses (Cox et al. 1982). Mechanical tillage disturbs surface soils and aids in rainwater infiltration (Jordan 1981), but seedings at creosotebush site were seldom successful and the treated area is usually reinvaded by creosotebush or annual forbs and grasses (Cox et al. 1984a). Pelleted tebuthiuron [N-(5-(1,ldimethylethyl)-1,3,4-thiadiazol2-yl)-WWdimethylurea] effectively controls creosotebush (Jacoby et al. 1982) and perennial grasses can be established if grass seeds and pellets are applied at the same time (Baur et al. 1977). Grass seedlings, however, may not survive if pellets are applied after seeds germinate because seedling roots encounter the herbicide as it moves through the upper soil profile (Baur 1979). The semidesert grasslands of the southwestern U.S.A. and northern Mexico are of great importance to the livestock industry, but the chances of reestablishing forage grasses are low because of erratic precipitation in summer. Therefore, it is important to address the effects of precipitation on plant establishment, persistence, and forage production. More than 300 forb, grass, and shrub species have been sown at 400 locations in the southwestern U.S.A. and northern Mexico during the past 90 years (Cox et al. 1982). A successful seeding was more likely to occur if seed of the following species were sown prior to the summer rains: (1) ‘A-68’ Lehmann lovegrass (Eragrostis lehmanniana), (2) ‘A-84’ and (3) ‘Catalina’ Boer lovegrass (E. curvula var. conferta), (4) ‘Cochise’ Atherstone lovegrass (E. lehmanniana X E. trichophera), (5) ‘S-75’ Kleingrass (Panicum coloratum), (6) ‘Premier’sideoats grama (Bouteloua curtipendula), and (7) ‘common’ buffelgrass (Cenchrus ciliaris). Researchers have evaluated either the relationships between mechanical seedbed preparation and grass establishment or chemical seedbed preparations and grass establishment, but have not attempted to directly compare both seedbed preparations. The purpose of this study was to compare establishment potential and persistence of 7 perennial grasses sown in mechanically and chemically prepared seedbeds.