Perennial Forage Stand Length Impacts on Spring Wheat Yields in a Semiarid Cropping System.

Perennial forages have the potential to diversify annual crop rotations and provide a number of ecosystem services. Yield benefits to the annual cash crop, often associated with soil-derived ecosystem services, have been observed with the inclusion of a perennial phase. Less is known, however, about the duration of and extent to which yield benefits are observed, which may depend upon the perennial crop type and duration of the perennial phase. Five perennial forages and forage combinations, alfalfa (Medicago spp.), intermediate wheatgrass (Thinopyrum intermedium (Host) Barkw. & D.R. Dewey subsp. intermedium), switchgrass (Panicum virgatum L.), intermediate wheatgrass-alfalfa mixture, switchgrass-alfalfa mixture, and an annual cropping system of continuous wheat (Triticum aestivum L.) were evaluated for their impacts on wheat yields in a six-year study conducted near Mandan, ND USA. Preliminary results indicate that spring wheat yields following at least two years of alfalfa were at least 120% higher than continuous spring wheat yields fertilized with 60lbs N. Additionally, spring wheat yields declined every year following conversion to annual crops. Mixtures of grass and alfalfa yielded 105 to 125% more spring wheat than fertilized spring wheat, but only after at least three years of a perennial phase. These results suggest the addition of perennials in annual crop rotations in semi-arid environments may provide yield benefits, but benefits may only be realized after two to three years of a perennial phase that should include a perennial legume such as alfalfa.