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United States Department of Agriculture

Agricultural Research Service

Research Project: Grass-Legume Mixtures to Enhance Sustainability of Irrigated Pastures

Location: Forage and Range Research

2013 Annual Report

1a.Objectives (from AD-416):
(1) Compare livestock performance, economics, and subsequent carcass characteristics from beef grazing grass monocultures and low- and high-tannin grass-legume mixtures versus traditional feedlot-based finishing; (2) Determine best possible grass-legume mixtures and plant densities that maximize pasture productivity and nutritional quality; and (3) Determine the effects of tannins on nutrient cycling in grazing systems.

1b.Approach (from AD-416):
To compare livestock performance, economics, and subsequent meat quality of beef produced from grass monocultures versus low- and high-tannin grass-legume mixtures.

(1) Determine if tall fescue (TF)-legume mixed pastures will enhance livestock performance (ADG, feed efficiency, intake, and nutrient digestibility) and to compare if the animal performance will be further improved when animals are grazed on TF-birdsfoot trefoil (BFT) mixed pasture; (2) Investigate in vitro fermentation characteristics of forage pastures used in grazing study with emphasis on microbial protein synthesis and ruminal fatty acid (FA) composition; (3) Assess how different compositions of pasture alter carcass characteristics and beef quality; (4) Determine the differences in the FA composition of beef from pasture-finished vs. feedlot-finished cattle and the time required for changes in FA composition to occur; and (5) Assess the economics and barriers to adoption of grazing-based beef production, develop an effective extension program to facilitate the adoption of grazing management for beef production, and create an awareness of the beneficial nutrient management and other environmental impacts of such an exchange.

3.Progress Report:

This agreement was entered into to study plant and animal components of grass-legume mixtures of which several components were evaluated during this fiscal year.

During FY-2013: A 2-yr grazing study was completed evaluating the effects of finishing beef cattle grazed on tall fescue (TF) pastures without or with nitrogen (N) fertilization on growth performance, ruminal fermentation, and carcass characteristics. Overall results indicate that N fertilization on TF affected ruminal fermentation increased growth. During FY2013, an additional manuscript was submitted to the journal entitled, “Professional Animal Scientist,” and two poster presentations were made at the 2013 ADSA-ASAS Meeting at Indianapolis.

A related study is now evaluating cattle performance when grazing grass-legume mixtures. During FY2013, the first year of this study was completed evaluating beef steers grazing tall fescue (TF) pastures with or without low- and high-tannin legumes and the resulting effects on growth performance, ruminal fermentation, and carcass characteristics. In response to grass-legume mixtures, the preliminary (1-yr) average daily gains (ADG) were 1.7, 1.4, 1.4, and 0.8 pounds per day for Tall fescue+Birdsfoot trefoil, Tall Fescue+Alfalfa, Tall Fescue+Nitrogren Fertilizer, and Tall Fescue-Nitrogren Fertilizer, respectively, with the Tall fescue no fertilizer being statistically lower than the other treatments. Forage yields followed a similar pattern with the Tall Fescue + fertilizer yield being the highest (4950 lbs/acre) but not significantly different than mixtures with alfalfa and birdsfoot trefoil, and all three being higher than Tall Fescue with no fertilizer (3591 lbs/acre). Carcass quality and forage yield and quality data are being analyzed. This study will be repeated for a second year. This research is being conducted in partial completion of a M.S. thesis and results were presented by the graduate student at the Western Society of Crop Science meetings in Pendleton, OR.

A small-plot of binary mixtures of five grasses [orchardgrass (OG), tall fescue (TF), meadow brome (MB), timothy, and perennial ryegrass (PR)] and three legumes [alfalfa (AF), birdsfoot trefoil (BF), and cicer milkvetch (CM)] were established previously. Ratios in the mixtures included 0, 25, 50, and 75% legume composition. Results revealed that tall fescue, OG, and MB grass-legume mixes averaged 6.0, 5.0, and 14.0% higher forage production than their respective grass monocultures. The highest seasonal forage production of TF combinations was 1.62 Mg/ha TF:AF (50:50), 1.63 Mg/ha TF:BF (75:25), and 1.64 Mg/ha TF:CM (75:25). Highest forage production of OG combinations was 1.10 Mg/ha OG:AF (50:50), 1.09 Mg/ha OG:BF (75:25), and 0.99 Mg/ha OG:CM (75:25). Highest seasonal forage production of MB combinations was 1.23 Mg/ha MB:AF (50:50), 1.25 Mg/ha MB:BF (75:25), and 1.11 Mg/ha MB:CM (75:25). These results suggest that grass-legume mixtures can be an effective strategy to improve pasture productivity. Mixtures with cicer milkvetch and birdsfoot trefoil were most productive when they constituted 25% of the mix, whereas, mixtures with alfalfa were most productive when it comprised 50% of the mix. This research was conducted in partial completion of a M.S. thesis, and was presented at two professional meetings.

Nutrient cycling data were collected in FY2013. Soil subsamples are analyzed for available nitrogen (ammonia and nitrate) and for total N by combustion. Leachate samples were collected every two weeks during the growing season. Samples will be analyzed for nitrate-nitrite. Plant samples, collected before and after each grazing event, are used to determine the nutrients removed in the forage. A mass balance approach comparing total nitrogen outputs against total nitrogen inputs for each treatment will be utilized to estimate losses due to volatilization. The effect of tannins on nitrogen cycling will be examined.

Last Modified: 4/20/2014
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