Fewer Greenhouse Gases Released When Cattle Graze on Legume-rich Grass Pastures Compared to Nitrogen Fertilized Pastures

October 31, 2017

GAINESVILLE, Florida – Beef cattle that graze on legume-enriched grass pastures release fewer greenhouse gases compared with the typical nitrogen fertilization regimes in the Southeastern U.S., based on the limited results of a Southern Sustainable Agriculture Research & Education (SSARE)-funded study at University of Florida.

The results offer a sustainable grazing management alternative for those farmers who are concerned about how their farming practices impact the environment, and want to increase production sustainability. Further research, however, is needed to quantify greenhouse gas emissions from other sources and during other seasons of the year.

“Most research about the adoption of legume plants into grass pastures concludes that the presence of legumes increases pasture nutritive value and sustainability of the system. However, presence of legumes may increase nitrogen content in animal urine and dung, and serve as a source of nitrous oxide (urine and dung) and methane (dung) emissions which are powerful greenhouse gases,” said Lynn Sollenberger, a forage management specialist with the University of Florida in Gainesville.

With an $11,000 SSARE Graduate Student Grant (GS15-151), “Legume Proportion of Grass-legume Mixtures Affects Greenhouse Gas Emissions from Animals Grazing Pasture,” graduate student Marta Kohmann, along with Sollenberger and Jose Dubeux, University of Florida forage specialist at the North Florida Research and Education Center, measured the quantity of greenhouse gas emissions from urine and dung of animals that grazed on legume-grass pastures and on grass pastures fertilized with nitrogen.

Results found that methane emissions from dung of animals grazing legume-rich pastures was 1.75 times greater than those grazing bahiagrass fertilized with nitrogen.

“Dung from animals grazing legume-grass pastures emitted more methane than that from animals grazing fertilized grass pasture, and this difference is likely related to the greater nitrogen concentration in the dung when legumes were part of the pasture,” said Kohmann.

However, once the researchers took into account nitrous oxide emissions from nitrogen fertilizer, they found that annual emissions from the bahiagrass pasture were 2.5 times greater than emissions from the legume-grass mixture.

“This difference could potentially be greater, since in these estimates we are not accounting for other emissions associated with nitrogen fertilizer, such as emissions from fertilizer production, storage, and transportation; and from fuel necessary for its application,” said Sollenberger. “In addition, methane emissions from enteric fermentation of animals grazing legumes are estimated by other researchers to be 20 percent less than those from animals grazing warm-season grasses.”

In addition, researchers found that nitrous oxide emissions from urine and dung of animals grazing either grass-fertilized or legume-grass mixed pastures were lower compared with what is used in national greenhouse gas emissions inventories of beef cattle.

“Current emission estimates from animal waste may be overestimated significantly for animals grazing on pasture,” said Sollenberger. “Our work provides researchers and producers with valuable information regarding sustainability of legume- and grass-based beef production systems in the Southeastern U.S. by quantifying greenhouse gases coming from excreta of beef cattle fed either of these diets.”

Published by the Southern Region of the Sustainable Agriculture Research and Education (SARE) program. Funded by the USDA National Institute of Food and Agriculture (NIFA), Southern SARE operates under cooperative agreements with the University of Georgia, Fort Valley State University, and the Kerr Center for Sustainable Agriculture to offer competitive grants to advance sustainable agriculture in America's Southern region. This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, through Southern Sustainable Agriculture Research and Education, under sub-award number: GS15-151. USDA is an equal opportunity employer and service provider. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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Topics: Grazing Management, Livestock, Natural Resources / Environment
Related Locations: South