Alfalfa yield and quality as influenced by establishment method

Weed control during alfalfa (Medicago sativa L.) establishment is a primary concern of forage producers. Companion crops and clearseeding with an herbicide are commonly used methods for establishing alfalfa. This study evaluated an alternative method in which alfalfa is seeded into a winter-killed mulch residue from a fall-seeded winter cover crop of oat (Avena saliva L.) and compared it with seven other establishment methods: (i) drilled with postemergence application of imazethapyr ((+/-)-2-[4,5-dihydro-4-methyl-4- (1-methylethyl)-5-oxo-2-imidazol-2-yl]-5-ethyl-3- pyridinecarboxylic acid), (ii) drilled with postemergence application of sethoxydim (2-[1-(ethoxyimino)butyl] 5-[2-(ethylthio)propo]-3-hydroxy-2-cyclohexen-1-one), (iii) drilled with no oat and no herbicide, (iv) oat companion crop harvested for silage, (v) oat companion crop harvested for grain, (vi) spring-planted oat drilled with postemergence application of sethoxydim, and (vii) broadcast seeding without weed control. Field studies were conducted at two Iowa locations in 1996 and 1997. The oat companion-crop treatment harvested for silage yielded the greatest forage dry matter (DM) in the establishment year. However, drilled treatments without an oat companion crop, including the control, resulted in greater alfalfa stand densities. Treatments with sethoxydim had lower grass weed densities in the establishment year while the drilled control and oat residue mulch treatment had the greatest. Treatments containing oat, and clear-seeded with imazethapyr, had the lowest broadleaf weed densities in the establishment year. During the establishment year, forage quality was greatest where alfalfa density was high and weed density was low. Because no significant yield or quality differences were found among treatments in the year after establishment, method chosen for establishment should be based on forage needs during the establishment year.