Date of Award:

5-2013

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant, Soils, and Climate

Committee Chair(s)

Earl Creech

Committee

Earl Creech

Committee

Michael Peel

Committee

Grant Cardon

Abstract

Managed pasture forms the foundation for much of the U.S. livestock iv production. Increased forage yield and quality can be achieved with nitrogen (N) fertilizer but increases the cost of pasture production. Rising prices of N have led to a return to the use of grass-legume pastures to reduce or replace commercial N fertilizer. There is a need to identify viable grass-legume mixtures and species planting ratios for the region of the Intermountain Western United States The purpose of this study was to identify grass-legume combinations and planting ratios that maximize forage production and forage quality in irrigated pastures. The grass-legume mixtures produced more forage than their respective unfertilized grass monocultures by 24% tall fescue (TF)-alfalfa (ALF), 19% TFbirdsfoot trefoil (BFTF), 35% meadow brome (MB)-ALF, 26% MB-BFTF, 41% orchardgrass (OG)-ALF, and 29% OG-BFTF. The CMV mixtures did not increase forage production compared to the unfertilized monoculture. The highest to lowest yielding grass mixtures were TF > MB > OG. The highest yielding legume mixtures were ALF > BFTF > CMV. The grass-legume mixtures had higher CP than the unfertilized mixtures by 37% TF-ALF, 21% TF-BFTF, 57% MB-ALF, 35% MB-BFTF, 47% OG-ALF, and 23% OG-BFTF. Cicer milkvetch only combined well with MB and may not be suitable for irrigated pastures. Individual harvests of the mixtures had similarly higher yields and CP, and lower NDF, than the unfertilized grass monocultures. Relative species composition had an effect on total forage yield, CP, and NDF. Additionally, the grass-legume mixtures of all species were most productive at the 50:50 planting ratio. In conclusion, the grass-legume mixtures were found to produce as much as a pasture fertilized at 134 kg N ha-1. Additionally, a grass-legume pasture will have much higher CP and lower NDF than a fertilized grass pasture. As a result, using grass-legume pastures will reduce or eliminate N applications while providing higher quality forage for livestock.

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