Establishing Native Perennial Bioenergy Crops with Cereal Grain Companion Crops

Abstract

Companion crops supply additional economic returns when used to establish perennial forage crops, and they should provide similar benefits when establishing native perennial grasslands for bioenergy. We evaluated the effect of cereal grains and native perennial companion crops on biomass yield of three different bioenergy crop types (switchgrass (Panicum virgatum (L.) Vitman) monoculture, four-species native grass mixture, and CP-25 polyculture mixture) during the seeding year and two subsequent harvest years at four environments. Effects of companion crops on bioenergy crop yields were inconsistent across locations and time, but some general patterns were observed. Averaged across all bioenergy crops, three companion cropping treatments—oat (Avena sativa L.), barley (Hordeum vulgare L.), and Canada wildrye (Elymus canadensis L.) harvested for forage—produced harvestable biomass during the seeding year while suppressing weeds and maintaining perennial biomass yield of the main crop during the first harvest year. Harvestable forage yields were greater for the oat companion crop compared to Canada wildrye during the seeding year at two environments, which could make the cereal grain companion crops more profitable for producers, depending on biomass markets. The polyculture crop yielded 33 and 39 % more perennial biomass than the switchgrass and grass mix in one environment and had 25 % less weed biomass compared to switchgrass in another. No individual companion crop/bioenergy crop combination consistently yielded more perennial biomass or less weed biomass compared to unweeded controls across all environments; however, companion crops can supply marketable grain and biomass during the seeding year when planted with native perennial grasslands without decreasing perennial biomass yields in subsequent harvest years.