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 NO3-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 NO3-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 NO3-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.