Productivity and sustainability of four grazed grass-alfalfa mixtures

Forage grasses need to be evaluated in pasture trials in the Great Plains r egion of North America. The objective of this study was to compare four gra ss-alfalfa (Medicago saliva L.) mixtures for productivity and persistence w hen grazed during spring and summer. The grasses were Altai wildrye (Leymus angustus [Trin.] Pilger), intermediate wheatgrass (Elytrigia intermedia [H ost] Nevski), meadow bromegrass (Bromus riparius Rehm. syn. B. biebersteini i Roem. & Schult.) and Russian wildrye (Psathyrostachys junceus [Fisch.] Ne vski), with grass rows seeded perpendicular to the alfalfa rows. Two sites, 4 km apart, were grazed with yearling beef cattle from 1987 to 1993. Forag e yield differed among grass treatments in 4 of 5 years, but differences we re inconsistent over time. Five-year mean forage yields and total livestock production were not significantly different among the four grasses. Mean a nnual forage yields ranged from 800 to 8170 kg ha(-1) and were related to t he amount of growing season (April-August) precipitation, Carrying capacity ranged from 35 steer grazing days per hectare in 1992 to 176 in 1991. Gras ses in the mixtures did have a significant effect on the grass-alfalfa rati o and on ground cover. Alfalfa content was highest when grown with Altai wi ldrye and lowest when grown with Russian wildrye. Percentage of ground cove r 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 conta ined the least alfalfa and weeds after 7 yr. Intermediate wheatgrass and Al tai wildrye did not compete with invading weeds at one site, or with alfalf a at the other, and should not be recommended for spring-summer pastures in semiarid regions. Meadow bromegrass maintained a balance of grass and alfa lfa and further research should confirm its persistence in semiarid climate s.