ALFALFA ESTABLISHMENT WITH BARLEY AND OAT COMPANION CROPS DIFFERING IN STATURE

Small-grain companion crops are commonly used for establishing forage legumes in the north-central USA. Semidwarf-stature barley (Hordeum vu lgare L.) and oat (Avena sativa L.) show promise as less competitive a nd more lodging-resistant companion crops. This study compared forage production and agronomic characteristics of companion-cropped semidwar f and conventional-stature genotypes of barley and oat. Alfalfa (Medic ago sativa L.) was seeded both with and without companion crops in exp eriments conducted at St. Paul, MN, from 1987 through 1989 on a Waukeg an silt loam soil (fine-silty over sandy or sandy-skeletal, mixed, mes ic Typic Hapludoll). Both semidwarf and conventional-stature barley an d oat genotypes were evaluated. Small-grain and alfalfa forage harvest s were made at the boot and soft dough stages of the small grain. Subs equent alfalfa harvests also were made later in the establishment seas on and at first flower in the following spring. Light penetration thro ugh the canopies of the various companion crops was monitored in all y ears. Weed biomass was measured in 1989, to estimate weed suppression by the companion crops. Light intensity at the level of the alfalfa wi thin the semidwarf companion crop canopy was consistently higher than within the conventional-stature companion crops. Averaged over all sma ll-grain genotypes, companion crop treatments produced from 202 to 235 5 kg ha(-1) more forage dry matter than direct-seeded alfalfa (no comp anion crop). Alfalfa dry matter production during establishment was su ppressed by all companion crops, especially those with conventional st ature. Weeds mere greatly suppressed by all companion crops. Companion crops increased mortality of alfalfa plants during establishment, but did not lower production of the alfalfa at subsequent harvests in the establishment season or in the following spring. Overall, semidwarf a nd conventional barley and oat were comparable in performance as compa nion crops in these studies, but semidwarf genotypes should prove part icularly advantageous under conditions where lodging is likely to occu r.