Weed Suppression in No-Till Alfalfa (Medicago sativa) by Prior Cropping of Summer-Annual Forage Grasses

Abstract

A sorghum-sudangrass hybrid [Sorghum bicolor(L.) Moench. xSorghum sudanense(P.) Stapf. ‘DEKALB SX17+’] (SSH) and foxtail millet [Setaria italica(L.) Beauv.] (FM) were evaluated for their effects on weed populations when grown for forage and as land conditioners prior to late-summer, no-till planting of alfalfa (Medicago sativaL. ‘Arc’). Both grasses established well in no-till situations, except for FM when excessive mulch impeded seed placement or seedling summer-annual weeds were not destroyed at planting time. SSH was the better competitor; after both were planted into a dense stand of seedling summer-annual weeds, SSH outyielded the weeds while FM did not. Both grasses suppressed weeds and enhanced subsequent alfalfa establishment. Obtaining adequate alfalfa stands was not a problem in no-till seedings: seedling populations often exceeded 300/m23 to 6 weeks after planting. Lack of adequate weed control was associated with stand losses in which disease was also a factor. Biennial and perennial broadleaf species were the predominant weeds. Prior cropping of SSH or FM is a valuable option for growers wishing to establish alfalfa without tillage, particularly when summer forage is useful.