Intermediate Wheatgrass + Legumes: Friends or Foes?.

The perennial cereal intermediate wheatgrass (Thinopyrum intermedium; IWG) represents a novel way to improve the sustainability of grain production by providing food for humans while increasing ground cover, soil organic matter, and soil nutrient retention. However, the environmental benefits of IWG may not be fully realized if external inputs of nitrogen (N) fertilizer are relied upon to maximize grain production, which could lead to the disruption of soil nutrient cycles, greater N leaching, and increased water pollution. Instead, intercropping IWG with legumes could provide a biological source of N for grain production while enhancing nutrient cycling and microbial activity. In Minnesota, a field study was undertaken to evaluate IWG grain production in non-fertilized and urea-fertilized monocultures, compared to bicultures of IWG and several perennial legume species, including alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus), Canada milk vetch (Astragalus canadensis), and clover (Trifolium spp.). While legumes were generally slow to establish in IWG, legume biomass production of all species was greater than 1500 kg ha^-1 the year following seeding, in second-year IWG stands. There was no relationship between legume biomass production and IWG grain yields among legume species, with the exception of white clover, where there was a positive relationship (r = 0.62; P = 0.013) between IWG grain yields and white clover biomass (Trifolium repens). Interactions between IWG and legume intercrops likely differ among legume species in terms of nutrient uptake and competition for resources, and early results suggest that interactions between IWG and white clover benefit grain yields the most, compared to other legume species. Research is ongoing to identify the effects of different legume intercrop species on IWG nutrient uptake and grain production, compared to chemically fertilized stands.