INTERCROPPING LEGUMES INTO SUNFLOWER AT DIFFERENT GROWTH-STAGES

Sunflower (Helianthus annuus L.) residue is fragile and does not provi de a lot of ground cover. Legumes intercropped in sunflower could incr ease soil cover, reduce soil erosion, and add nitrogen and organic mat ter to the soil. Field studies were designed to evaluate the effect of different sowing dates of hairy vetch (Vicia villosa Roth), yellow-fl owered sweetclover (Melilotus officinalis Lam.), alfalfa (Medicago sat iva L.), snail medic [Medicago scutellata (L.) Mill.], and black lenti l (Lens culinaris Medik.) intercropped in dwarf and standard-height oi lseed sunflower an agronomic traits of sunflower. Legumes were sown th e same time as sunflower and at the V4 and V10 sunflower growth stages . Studies were conducted at Carrington (1992 and 1993) and Prosper (19 92, 1993, and 1994), North Dakota. Sunflower oil content was not influ enced by intercropped legumes. When sown at the same time as sunflower , all legumes, except black lentil, reduced sunflower seed yield. Blac k lentil produced 1385 kg ha(-1) dry matter. Compared with the control , sunflower achenes per head, and head diameter were reduced by legume s sown at the same time as sunflower. Sunflower yield, head diameter, achenes per head, and 1000-achene weight were not significantly lower than legumes were sown at the V4 or V10 sunflower growth stages. Hairy vetch is recommended for intercropping at V4 and V10 sunflower growth stages because in did not reduce sunflower yield and on average produ ced 1593 and 831 kg ha(-1) dry matter. At the drier environment, Carri ngton 1992, biomass produced by the legumes was low when legumes were sown at the V4 or V10 sunflower growth stages, with 314 and 57 kg ha(- 1), respectively. Sweetclover could be sown at the V4 growth stage of sunflower to establish it as a cover crop for the subsequent season.