Forage boost or grain blues? Legume choices shape Kernza intermediate wheatgrass dual-purpose crop performance

Kernza intermediate wheatgrass is a new perennial grain crop with the potential to produce high nutritive value forage when intercropped with legumes. Understanding the potential benefits of intercropping systems requires considering the interaction between different legume species intercropped, intermediate wheatgrass row spacing, and environments encompassing spatial and temporal variation. We aimed to evaluate the effect of these factors on the biomass allocation to harvestable (grain, intermediate wheatgrass forage, legume forage) and non-harvestable (weed biomass) outputs. In four environments, given by the combination of two sites (Wisconsin, USA) and two establishment years, we sowed intermediate wheatgrass in two row spacings in eight cropping systems: three intermediate wheatgrass monocultures control without N fertilization, intermediate wheatgrass fertilized with 45 or 90 kg N ha−1 as urea, and four intermediate wheatgrass-legume intercrops (intermediate wheatgrass with alfalfa, Berseem clover, Kura clover, or red clover). We evaluate grain yields, intermediate wheatgrass and legume forage, and weed biomass over three consecutive years. Our results suggest that intercropping legumes does not affect Kernza grain yield in the first grain production year, which is the year with the highest yield potential. In subsequent production years, grain yields were lower in red clover intercrops than in intermediate wheatgrass monoculture control or fertilized, depending on the environment. Among the legumes tested in our study, red clover and alfalfa were suitable for increasing total biomass production in most of the environments and red clover reduced weed biomass compared to intermediate wheatgrass monocultures. Our results encourage intercropping legumes with intermediate wheatgrass because of the increase in forage yield and quality. These benefits can compensate for lower Kernza grain yields commonly observed in the second and third production years. Our study provides valuable insights into the intermediate wheatgrass potential as a dual-use crop for grain and forage production. Improving our understanding of the factors that influence grain yield and forage production such as post-harvest management, multiple forage harvests or grazing, may optimize the productivity and sustainability of these cropping systems.