ALFALFA Alfalfa Yield and Quality as Influenced by Establishment Method

management of a companion crop is critical to successful establishment of perennial forages (Albrecht and Hall, Weed control during alfalfa (Medicago sativa L.) establishment is 1995). a primary concern of forage producers. Companion crops and clearWeed management is important for decreasing comseeding with an herbicide are commonly used methods for establishing alfalfa. This study evaluated an alternative method in which alfalfa petition with alfalfa and for increasing alfalfa yield and is seeded into a winter-killed mulch residue from a fall-seeded winter quality during the establishment year (Chapko et al., cover crop of oat (Avena sativa L.) and compared it with seven other 1991; Hall et al., 1995). Weed control, during legume establishment methods: (i) drilled with postemergence application of establishment without a companion crop, is critical to imazethapyr {( )-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxoobtain a productive stand (Zollinger and Meyer, 1996). 2-imidazol-2-y1]-5-ethyl-3-pyridinecarboxylic acid}, (ii) drilled with Herbicide use, when seeding alfalfa alone, reduces weed postemergence application of sethoxydim {2-[1-(ethoxyimino)butyl] densities and allows better stands of pure alfalfa to be 5-[2-(ethylthio)propo]-3-hydroxy-2-cyclohexen-1-one}, (iii) drilled with obtained in the seeding year (Schmid and Beherns, no oat and no herbicide, (iv) oat companion crop harvested for silage, 1972). Competition, provided by weeds or companion (v) oat companion crop harvested for grain, (vi) spring-planted oat crops, reduces the total season alfalfa yield compared drilled with postemergence application of sethoxydim, and (vii) broadcast seeding without weed control. Field studies were conducted at two with alfalfa seeded alone with an herbicide (Sheaffer Iowa locations in 1996 and 1997. The oat companion-crop treatment et al., 1988). Lanini et al. (1991) found similar weed harvested for silage yielded the greatest forage dry matter (DM) in percentages in alfalfa treatments established with a comthe establishment year. However, drilled treatments without an oat panion crop or alone with an herbicide. Weed control companion crop, including the control, resulted in greater alfalfa stand during establishment also increased alfalfa shoot weight densities. Treatments with sethoxydim had lower grass weed densities and leaf number (Stout et al., 1992). in the establishment year while the drilled control and oat residue Clear-seeding is a planting method that provides an mulch treatment had the greatest. Treatments containing oat, and alternative to using a companion crop. This method clear-seeded with imazethapyr, had the lowest broadleaf weed densiprovides decreased competition from companion crops ties in the establishment year. During the establishment year, forage and increases in harvested alfalfa yields in the establishquality was greatest where alfalfa density was high and weed density was low. Because no significant yield or quality differences were found ment year (Simmons et al., 1992). Herbicides are necesamong treatments in the year after establishment, method chosen for sary for weed control and are advantageous for firstestablishment should be based on forage needs during the establishyear yields of clear-seeded alfalfa (Sheaffer et al., 1988). ment year. Imazethapyr is a postemergence selective herbicide that was labeled for use on alfalfa in January 1995 (Dahmer, 1995). Imazethapyr gives excellent control of annual A has traditionally been established in the grass and broadleaf weeds. Some short-term plant stuntMidwest with a companion crop such as oat (Chapko ing, however, can occur for alfalfa plants, but this does et al., 1991; Simmons et al., 1995). Companion crops not lead to phytotoxic effects by harvest time (Zollinger are advantageous to alfalfa during establishment beand Meyer, 1996). cause they suppress weed germination, growth, and A method of establishing alfalfa that utilizes the attricompetition and decrease the potential for soil erosion butes of both companion cropping and herbicide use (Wollenhaupt et al., 1995). Companion crops can inwas introduced in the late 1980s (Twidwell et al., 1993). crease total dry matter (DM) production during the Sethoxydim is a postemergence herbicide that can be establishment year (Sturgul et al., 1990; Chapko et al., used during alfalfa establishment to control grass weeds 1991). Companion crops can also negatively affect alor oat (Twidwell et al., 1993). Sethoxydim application falfa during establishment by competing for light, moisto alfalfa and oat is very effective in killing the companture, and nutrients, which can lead to reduced yield ion crop and other grass weeds that might be present. (Hall et al., 1995) and decreased plant density (Lanini This provides a pure stand of high quality alfalfa forage et al., 1991; Nickel et al., 1990). Appropriate harvest for harvest (Stute and Posner, 1993). A postemergence application of sethoxydim to oat growing with alfalfa can also optimize alfalfa yields in the establishment year Dep. of Agron., Iowa State Univ., Ames, IA 50011-1010. Journal (Curran et al., 1990; Twidwell et al., 1993). Another Paper no. J-18704 of the Iowa Agric. and Home Econ. Exp. Stn., Ames. Project no. 2899, supported by Hatch Act and State of Iowa funds. Received 25 Aug. 2000. *Corresponding author (kjmoore@ Abbreviations: ADF, acid detergent fiber; ADL, acid detergent lignin; iastate.edu). CP, crude protein; DM, dry matter; IVDMD, in vitro dry matter digestibility; NDF, neutral detergent fiber. Published in Agron. J. 94:65–71 (2002).