Franco, J. G., Duke, S. E., Hendrickson, J. R., Liebig, M. A., Archer, D. W., and Tanaka, D. L.
Perennial forages have the potential to diversify annual crop rotations and provide yield benefits to subsequent cash crops. Little is known about the duration of and extent to which yield benefits are observed in semiarid no-till systems following perennial forages, which may depend on the perennial crop type and duration of the perennial phase. Five perennial forage and forage combinations, alfalfa (Medicago sativa L.; PALF), intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey subsp. Intermedium; IMWG], switchgrass (Panicum virgatum L.; SWG), alfalfa--intermediate wheatgrass mixture (PALF+IMWG), alfalfa--switchgrass mixture (PALF+SWG), and an annual cropping system of continuous spring wheat (Triticum aestivum L.) fertilized with 67 kg ha-1 of N (CWF) were evaluated for their impacts on wheat yields in a 7-yr study conducted near Mandan, ND. Wheat yields following 2 yr of alfalfa were comparable to CWF, and 3 and 4 yr of alfalfa, respectively, were 19 and 41% higher. After 5 yr of PALF+SWG, which was primarily comprised of alfalfa, wheat yields were 23% higher than CWF, and comparable to CWF after 3 and 4 yr in PALF+SWG. Four years in PALF+IMWG were needed to produce wheat yields comparable to CWF. Yield benefits persisted for up to 3 and 4 yr following 3 yr of PALF or 5 yr of PALF+IMWG, respectively. Overall, alfalfa and alfalfa--perennial grass mixtures showed the greatest promise for enhancing yields. These results indicate that a perennial phase of at least 2 yr is needed to provide yield benefits to subsequent no-till annual crops. [ABSTRACT FROM AUTHOR]