Performance of wheatgrasses and wheatgrass-sainfoin mixtures under three schedules of sheep defoliation

The role of cool-season perennial forages in extending the grazing season on the Southern High Plains of Texas was evaluated during 2 yr. Each of 'Hycrest' crested (Agropyron cristatum x A. desertorum)'Jose' tall (Thinopyrum ponticum), and 'Luna' pubescent (T. intermedium subsp. barbulatum) wheatgrasses was grown in monoculture and in binary mixture with 'Renumex' sainfoin (Onobrychis viciifolia), a non-bloating legume. Objectives were to determine the productivity, quality, water use efficiency, and animal utilization of forages when grazing by sheep was initiated at different times in spring. Early, mid, and late dates of initial spring grazing (harvests) by sheep corresponded to vegetative, elongating, and post-heading phonological stages of the grasses. Swards were rotationally grazed to a high level of utilization within 4 days; second growths were grazed 6 to 10 wk after first growths.

Mixture productivity was similar to or below that of monocultures. Jose had higher season mean production than Luna and Hycrest in both yr; values ranged from 3316 to 4492 kg ha-1. Quantity of herbage utilized during grazing was 13 to 29% greater in mixtures than in monocultures at all harvests except first, 1986. Total season utilization, ranging from 3956 to 5031 kg ha~, was greatest for mid or late dates of initial harvest in both yr and was higher in 1985 for Jose than for other species. Water use efficiency (1986 only), ranging from 10 to 34 kg ha~ mm", was higher for Jose than for other species at second harvest and for early than for late dates at both harvests.

Organic matter digestibility (OMD) of Hycrest exceeded that of other grasses by at least five percentage units at all harvests, while OMD of Jose was consistently below that of other grasses at second harvests, by the same amount. Mean OMD of sainfoin was usually lower than the mean for grasses, by 4 to 12 percentage units. Rate of organic matter intake was 23 to 34% higher for mixtures than for monocultures at all harvests except first, 1986.

Results indicate greater carrying capacity and potential individual animal performance for mixtures than for monocultures; mixtures with Hycrest are expected to maximize individual animal performance while those with Jose maximize carrying capacity.