Green‐Manure Legume Effects on Soil Nitrogen, Grain Yield, and Nitrogen Nutrition of Wheat

Knowledge of legume N production and legumeffects on subsequent crop yield and quality is necessary to encourage legume use instead of the traditional fallow on set‐aside land. Objectives of these studies were to: (i) compare seeding‐year herbage and N yields five forage legume species, (ii) determine soil NO 3 ‐N status in the spring following green‐manure legume crops, and (iii) evaluate effects of green‐manure legumes on grain yield, grain yield components, and N nutrition of the subsequent wheat ( Triticum aestivum L.) crop when fertilized with 0, 75, and 150 kg N ha −1 . Field experiments were conducted on a Fargo silty clay (fine, montmorilloritic, frigid Vertic Haplaquoll) at Fargo and on a Perella‐Bearden silty clay loam (fine‐silty, mixed, frigid Typic Haplaquoll, fine‐silty, frigid Aeric Caiciaquoll) near Prosper, ND, during 1984 to 1986. All legume species had equal herbage and N yields across the four environments and were greater than the wheat‐straw check. Accumulated legume herbage and fall regrowth were incorporated into the soil in late fall. Spring soil NO 3 ‐N following Terra Verde alfalfa ( Medicago sativa L.) and hairy vetch ( Vicia villosa Roth.) was equal to the fallow check and greater than the soil NO 3 ‐N following the wheat check or other legume species. Grain yield, grain N, and N uptake of unfertilized wheat following the legume treatments generally were similar to those following fallow and wheat fertilized with 150 kg N ha −1 . Increases in all grain yield components following legumes contributed to this yield advantage. Efficiency and utilization of N generally were greater following a green‐manure crop than following either fallow or wheat checks. This study suggests that green‐manure legumes should be considered as an alternative to fallow on set‐aside land in higher moisture areas.