Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Plants, Soils, and Climate

Committee Chair(s)

J. Earl Creech


J. Earl Creech


Michael D. Peel


Grant E. Cardon


Pastures in the Intermountain Western United States mainly consist of cool-season grasses which lack production without supplemental nitrogen. Legumes provide nitrogen at reduced cost compared to nitrogen fertilizer. There is a need for proven methods of inter-seeding legumes into existing cool-season grass pastures as well as knowledge of how animals prefer legumes to grasses and how the nutritive value of forages change throughout the growing season. This research provides a resource for effective integration of legumes into pastures of the Intermountain West. Alfalfa, birdsfoot trefoil, and cicer milkvetch were inter-seeded into existing cool-season grass pastures following pretreatments of light tillage, mowing and glyphosate. Early spring and fall inter-seeding was unsuccessful, while late spring was moderately successful with overall alfalfa frequency of 30% after a year. Summer inter-seeding was the most successful with birdsfoot trefoil, alfalfa, and cicer milkvetch frequency of 42, 32, and 22%, respectively. In the animal preference study, when compared to tall fescue, birdsfoot trefoil was always utilized more.In most observations birdsfoot trefoil utilization was higher than orchard grass. While in all comparisons with meadow bromegrass there was no difference in utilization. During early growth, perennial ryegrass utilization was higher than birdsfoot trefoil utilization, but no difference in utilization was detected in later observations. Overall, birdsfoot trefoil was utilized 73% overall while grass utilization was 74, 67, 64, and 53% for perennial ryegrass, meadow bromegrass, orchardgrass and tall fescue, respectively. The interaction of growth stage and time of season on the nutritive value of alfalfa, birdsfoot trefoil, cicer milkvetch, orchardgrass, perennial ryegrass and tall fescue was determined. In the spring to early summer, legume nutritive value decreased rapidly with maturity, in midsummer the nutritive value decreased slowly with maturity, while in late summer the nutritive value remained stable. In the spring, grass nutritive value decreased rapidly, while in mid to late summer all grass regrowth was vegetative and the nutritive value remained stable. By inter-seeding in the summer, effectively managing mixed pastures, and utilizing forage at its highest nutritive value, legumes can benefit the pastures of the Intermountain West.