Productivity and sustainability of four grazed grass--alfalfa mixtures

Forage grasses need to be evaluated in pasture trials in the Great Plains region of North America. The objective of this study was to compare four grass-alfalfa (Medicago sativa L.) mixtures for productivity and persistence when grazed during spring and summer. The grasses were Altai wildrye (Leymus angustus [Trin.] Pilger), intermediate wheatgrass (Elytrigia intermedia [Host] Nevski), meadow bromegrass (Bromus riparius Rehm. syn. B. biebersteinii Roem. & Schult.) and Russian wildrye (Psathyrostachys junceus [Fisch.] Nevski), with grass rows seeded perpendicular to the alfalfa rows. Two sites, 4 km apart, were grazed with yearling beef cattle from 1987 to 1993. Forage yield differed among grass treatments in 4 of 5 years, but differences were inconsistent over time. Five-year mean forage yields and total livestock production were not significantly different among the four grasses. Mean annual forage yields ranged from 800 to 8170 kg ha(-1) and were related to the amount of growing season (April-August) precipitation. Carrying capacity ranged from 35 steer grazing days per hectare in 1992 to 176 in 1991. Grasses in the mixtures did have a significant effect on the grass-alfalfa ratio and on ground cover. Alfalfa content was highest when grown with Altai wildrye and lowest when grown with Russian wildrye. Percentage of ground cover by the grass plus alfalfa increased from an average of 3.8% in 1987 to 16.1% at one site and 31.9% at the second site by 1993. Russian wildrye contained the least alfalfa and weeds after 7 yr. Intermediate wheatgrass and Altai wildrye did not compete with invading weeds at one site, or with alfalfa at the other, and should not be recommended for spring-summer pastures in semiarid regions. Meadow bromegrass maintained a balance of grass and alfalfa and further research should confirm its persistence in semiarid climates.