INTERCROPPING ANNUAL MEDIC WITH CONVENTIONAL HEIGHT AND SEMIDWARF BARLEY GROWN FOR GRAIN

Interseeding annual legumes with grain crops has been proposed as a cr opping strategy to enhance ground cover, thereby reducing weed competi tion, suppressing soil erosion, and providing N for use by subsequent crops. The potential of annual medics (Medicago spp.) for intercroppin g in small-grain cropping systems has not been adequately assessed for the north-central United States. Our objective was to evaluate a spri ng barley (Hordeum vulgare L.)-annual medic intercrop system for barle y grain yield, fall biomass production, suppression of fall weeds, and quantity of N available for incorporation into the soil. Field experi ments were conducted in four Minnesota environments (Becker, Morris, R osemount, and St. Paul). Conventional height 'Robust' and semidwarf 'R oyal' barley were intercropped with each of three medic species ['Geor ge' black medic (M. lupulina L.), 'Mogul' barrel medic (M. truncatula Gaertn.) and 'Santiago' burr medic (M. polymorpha L.)]. Intercropping with medics reduced barley yields by an average of 6% at Rosemount, 30 % at St. Paul, and 76% at Becker, compared with monoculture barley fer tilized with N. Medics increased yields by 9% at Morris. Intercropping with medic reduced fall weed mass by an average of 65% across environ ments, compared with the fertilized Royal monoculture. Nitrogen availa ble for incorporation from the barley-medic intercrops ranged from 66 to 140 kg ha(-1) over the environments, whereas N available for incorp oration from fertilized barley monoculture ranged from 22 to 80 kg ha( -1) We conclude that the prospects for successfully intercropping with annual medic in a barley grain production system are mixed and depend in part on the medic species used and barley stature. A wider array o f medic types should be evaluated for their suitability in intercroppi ng with small grains.