Harvesting forage of the perennial grain crop kernza (Thinopyrum intermedium) increases root biomass and soil nitrogen cycling

Emerging perennial grain crops yield less grain than annual crops, but the economic viability of these perennial systems could be improved if both forage and grain are harvested. However, the belowground consequences of forage removal in perennial grain systems are unknown. This study aimed to determine the effect of the additional harvest of forage biomass on overall plant biomass allocation and labile soil C and N dynamics within a perennial grain dual-use system. Plant biomass and associated soil samples of a perennial grain [Kernza (Thinopyrum intermedium)] were taken monthly over the first three growing seasons under three harvest regiments: No Cut (0x), Summer Cut (1x), and Summer and Fall Cut (2x). The harvesting of forage biomass significantly increased both above- and belowground biomass. The once and twice forage-harvested treatments averaged 39% and 73% greater root biomass in 2016 and 39% and 49% greater root biomass in 2017 relative to the treatment not harvested for forage. Soil indicators of carbon and nitrogen storage were not affected by forage harvest but mineralizable carbon, an indicator of nutrient cycling, was greater under the forage harvested treatments. The harvest of forage and grain promoted nutrient availability and overall productivity (forage, root and grain biomass) relative to harvesting for grain only. Our findings suggest dual-use management of Kernza can provide a productive and profitable pathway for perennial grain adoption.