Date of Award:

5-1-2014

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

J. Earl Creech

Abstract

Tall fescue is the one of most common grasses in irrigated pastures throughout the Intermountain West. Two limitations of tall fescue are a decrease in productivity during hot summer months and the need for supplemental nitrogen (N). The objective of this research was to compare tall fescue-alfalfa (TF+ALF), tall fescue-birdsfoot trefoil (TF+BFT), tall fescue-nitrogen fertilizer (TF+N), and tall fescue without nitrogen fertilizer (TF-N) on forage yield, nutritional quality, and livestock performance. Research plots were established at the Utah State University Pasture Research Facility in Lewiston, UT in 2010 and grazed in 2012 and 2013. Treatments were arranged in a randomized complete block design with four replications and divided into four paddocks per replication. Three Angus crossbred steers with an average starting weight of 380 kg were placed on each treatment and rotated to a new paddock every 7 days. A put-and-take method was used throughout the growing season such that each paddock received 80% utilization. Four forage samples were collected from each paddock just prior to grazing using a 0.5 m2 quadrat for determination of dry matter (DM)

and nutrient content. ADF, NDF, IVTD, and TDN were used to estimate nutrient content and steers were weighed every 28 days to determine livestock performance. Forage yield was highest (P<0.05) in TF+N (5164 kg ha-1), followed by the TF+BFT (4721 kg ha-1) and TF+ALF (4463 kg ha-1) treatments, whereas, the TF-N treatment had the lowest yield (2920 kg ha-1). In this study, TF+BFT (593 g kg-1) and TF+ALF (593 g kg-1) had a better (P≤ 0.05) season-long average TDN value than TF+N (558 g kg-1), which in turn was higher (P≤ 0.05) than TF-N (550 g kg-1). Steer average daily gains (ADG) were different (P<0.05) in every treatment with TF+BFT (0.73 kg d-1) being the highest, followed by TF+ALF (0.67 kg d-1), then TF+N (0.61 kg d-1), and similar to forage yield, TF-N had the lowest ADG (0.40 kg d-1). Tall fescue greatly benefits from added N whether via fertilizer or N transfer by legumes and this study showed that BFT and ALF mixed with TF increases plant and animal performance while reducing fertilizer costs and helps maintain a more environmentally sustainable pasture.

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