Intercropping red clover with intermediate wheatgrass suppresses weeds without reducing grain yield

Intermediate wheatgrass (IWG) [Thinopyrum intermedium (Host) Barkworth & Dewey] is the first commercially produced perennial grain crop in the United States. Intercropping legumes with IWG has the potential to enhance dual-purpose grain and forage production and contribute to weed control in organic management systems. We compared IWG with annual winter wheat (Triticum aestivum L.) in monoculture and intercropped with red clover (Trifolium pratense L.) in a 3-yr experiment in central New York. Grain yield of IWG was lower than wheat in all years, partly due to lower tiller fertility and seed size in IWG. Compared with grain yield of 1,212 kg ha(-1) in the first year, IWG grain yield was 83% (202 kg ha(-1)) and 64% lower (441 kg ha(-1)) in the second and third years, respectively. Intermediate wheatgrass straw production increased 40% from 5,541 to 7,785 kg ha(-1) over 3 yr while wheat straw yield declined from 5,167 to 3,533 kg ha(-1). Red clover did not affect grain or straw yield of either crop but reduced weed biomass and weed species richness. Weed communities in IWG plots were dominated by perennial grasses by the second year of production, whereas annual weeds were dominant in wheat throughout the experiment. Preventing establishment of perennial weeds that will persist in perennial grain cropping systems should be a management priority. High forage production observed when comparing IWG and wheat suggest opportunities for including IWG in integrated crop-livestock systems where IWG's higher forage yield and quality has higher utility.