Forage nutritive value and predicted fiber digestibility of Kernza intermediate wheatgrass in monoculture and in mixture with red clover during the first production year

Kernza intermediate wheatgrass is the first perennial grain crop in the world and has been developed with conventional breeding to increase seed yield of forage intermediate wheatgrass (Thinopyrum intermedium (Host) Barkworth & D.R. Dewey). When managed for dual-use (grain and forage), Kernza intermediate wheatgrass can produce grain, crop residue (straw) in the summer, and green forage in the spring and fall. Mixtures of this grass with legumes could increase forage yield and nutritive value and provide other environmental and economic benefits. Despite the growing interest in these dual-use production systems, forage nutritive value of Kernza intermediate wheatgrass forage in a dual-use system in the Upper Midwest is unknown. A replicated field experiment was established in two locations in southern Wisconsin (Arlington and Lancaster) with two treatments: Kernza intermediate wheatgrass grown in monoculture and mixture with red clover (Trifolium pratense L.). Forage samples were collected at late vegetative stage in the spring, at grain harvest in the summer, and at the end of the regrowth period in the fall. Forage nutritive value of the monoculture was greatest in the spring with 456, 249 and 225 g kg−1 for neutral detergent fiber (NDF), acid detergent fiber (ADF) and crude protein (CP), respectively; lowest in the summer with 702, 427 and 51 g kg−1 NDF, ADF and CP, respectively, and intermediate in the fall with 590, 337 and 119 g kg−1 NDF, ADF and CP, respectively. Predicted total-tract neutral detergent fiber digestibility (ttNDFD) was 0.53 for the spring forage and averaged 0.37 for the summer and fall forage, with no differences between the mixture and monoculture. The relative forage quality (RFQ) for the monoculture was 175 for the spring forage, 65 for the summer residue, and 116 for the fall. Intercropping red clover with Kernza intermediate wheatgrass increased CP of the summer crop residue by 69%, and increased CP and RFQ of the fall forage by 49% and 11%, respectively, while reducing NDF and ADF of the fall forage by 25% and 18%, respectively. Therefore, Kernza intermediate wheatgrass forage is suitable for lactating beef cows, dairy cows, and growing heifers when harvested in the spring and fall, and it offers high potential for dual-use grain and forage systems.