Effective weed suppression in dual‐use intermediate wheatgrass systems

Abstract

AbstractIntermediate wheatgrass [IWG; Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] is a cool‐season perennial forage grass bred for higher seed yield. It is the first perennial grain crop in the United States, commercialized as Kernza since 2015. Managing IWG as a dual‐use grain and forage crop could provide several ecosystem services including conserving soil and clean water while increasing economic income to growers. However, little is known about the weed management risks associated with IWG. Therefore, we studied weed community composition, biomass, IWG grain, and aboveground biomass in a factorial experiment with two weed management treatments, two nitrogen fertilization rates, and four forage harvest schedules (no harvest, summer only, summer + fall, and spring + summer + fall). Over three production years, weed biomass decreased by 88% regardless of treatment, and the weed community composition changed from predominantly winter annual to perennial species. In the second and third production years the weed community composition remained relatively stable. Grain yield was 16% greater with 135 kg N ha−1 than 90 kg N ha−1 but was not affected by in‐season forage harvest or weed management treatments in the second and third years. Grain yield decreased from 763 to 371 kg ha−1 over three years, while aboveground biomass remained stable. Weed presence did not affect yields in second and third years. Dual‐use IWG cropping systems effectively suppressed weeds and IWG is a promising grain crop alternative for farmers interested in diversifying their cropping systems under similar conditions.