Reseeding by Eight Alfalfa Populations in a Semiarid Pasture

Abstract

Eight nlfnlfa populations were seeded in a dryland pasture in northern Utah. Densities of mature plants, seeds, seedlings, and l-year-old plants were measured in each of 3 years. The populations did not differ for mature plant stands or seed production. There was a higher rate of seedling survival for populations that primarily originated from Medicago sativu rather than M.falcata. All populations had some one-year-old plants persisting to replace mature plants killed by disease or rodents. Alfalfa (Medicago satin and A4. falcata) is a valued component of pastures in subhumid environments. Its contribution to livestock production in dryland pastures and modified rangelands of semiarid areas is less well documented, although Townsend et al. (1975) regarded alfalfa as one of the most promising forage legumes for dryland seedings in the Great Plains. Hervey (1960) reported that lamb gains increased after alfalfa and crested wheatgrass (Agropyron desertorum) were interseeded into native sod in Wyoming. The introduction of the dryland alfalfa cultivar ‘Nomad’was one of the most successful techniques used to improve antelope (Antilocapra americana) ranges in southeastern Oregon (Yoakum 1979). After 36 separate aerial seedings on more than 26,000 ha, alfalfa constituted 10% of the vegetation present for 6 years or longer. Lee and Rothwell (1966) and Norman (1968) successfully used alfalfa pasture to supplement native pasture for sheep and cattle in Australia. Vallentine et al. (1963) recommended the use of alfalfa in sagebrush zone range sites in Utah where annual precipitation averaged 30 cm or more. The merit of using alfalfa for supplementing native pasture or for interseeding will depend on the longevity of plants and the ability of the species to reseed in a droughty environment while subjected to grazing. Kilcher and Heinrichs (1965), Pearse (1965), and Rumbaugh and Pedersen (1979) presented evidence that alfalfa lived up to 23 years in environments that received 20 to 30 cm average annual precipitation. Gomm (1974) reviewed results from more than 50 seeding experiments on 1 I vegetation types in dryland areas of Montana. Annual precipitation at the study locations ranged from an average of 20 to more than 50 cm. Alfalfa either failed to become established or the stands declined rapidly in more than half of these plantings. The causes of the declining stands were not stated. Author is research geneticist, U.S. Dep. Agr., Agr. Res. Serv., Crops Research Laboratory, Utah State University, UMC 63, Logan, Utah 84322. This study is a contribution from the U.S. Dep. Agr., Agr. Res. Serv., in coopcration with the Utah Agricultural Experimental Station, Logan, Utah. Journal Paper No. 2525. Manuscript received May 2, 1980. 84 Gomm (1964) did find that ‘Ladak’ alfalfa and ‘Madrid’ sweetclover (Melilotus officinalis) established equally well in a dryland experiment where the seedbed was prepared with a moldboard plow. Nichols and Johnson (1969)concluded that biennial sweetclover was well adapted as a legume for rangelands with heavy clay soils in western South Dakota whereannual precipitationaveraged 39 cm. Natural reseeding was successful every 2 years and sufficient hard seed remained in the soil to safeguard against elimination of the species in a season when drought killed the seedlings. They believed that periodic seedset would provide sweetclover stands whenever growing conditions were suitable. Similar data and observations with alfalfa have not been reported. A mature stand of alfalfa in northern Utah was available as a study site to provide such information.