Cattle urine's planet-warming power can be curtailed with land restoration

When cow urine falls on degraded land, it releases far more nitrous oxide — a potent greenhouse gas — than when absorbed by healthy pasture; the findings show additional benefits of landscape restoration and conservation

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Credit: Neil Palmer/CIAT

The exceptional climate-altering capabilities of cattle are mainly due to methane, which they blast into the atmosphere during their daily digestive routine. Cattle urine is a lesser-known climate offender. It produces nitrous oxide (N2O), which has warming power far greater than that of carbon dioxide (CO2), the main driver of global warming. A study conducted by the International Center for Tropical Agriculture (CIAT) and partners shows that these N2O emissions can be significantly curbed by healthy cattle pastures.

For the study, researchers collected urine from cattle at research sites in five countries across Latin America and the Caribbean. They spilled these 500 mL samples on paired cattle fields classified as degraded or healthy, which was determined by vegetation coverage. In six of the seven test sites, degraded pastures emitted significantly more N2O – sometimes up to three times as much. The results were published January 29 in Scientific Reports, an open-access journal by the publishers of Nature.

“Degraded pastures are bad in so many ways,” said Ngonidzashe Chirinda, a CIAT researcher and the study’s lead author. “This study adds to the case for land restoration. Degraded pastures not only affect food security and the livelihood of farmers today, but affects the livelihood of future farmers because they emit more gases that cause global warming.”

The results add urgency to global land restoration agreements, including Initiative 20×20, which aims to bring into restoration 20 million hectares of land into restoration in Latin America by 2020 as a first major step toward even more ambitious restoration targets.

Estimates vary, but Chirinda calculates, conservatively, that there are 150 million hectares of degraded lands in Latin America. Brazil alone is home to some 80 million hectares of degraded pastureland.

Degraded livestock land is generally characterized by overgrazing, soil compaction, loss of organic material and low levels of nutrients and soil carbon. Large-scale land restoration with improved forage grasses, rotational grazing and the addition of shrubs and trees (silvopastoral farming) could significantly mitigate the negative climate effects wrought by degradation. In addition to reducing N2O emissions, restored landscapes generally contain more carbon, have healthier soils and more robust and productive livestock.

“This study highlights the importance of avoiding land degradation in the first place,” said Todd Rosenstock, a co-author based at World Agroforestry (ICRAF). “Maintaining healthy pastures appears to reinforce goals of both the United Nations’ Framework Convention on Climate Change and the UN Convention to Combat Desertification simultaneously.”

The curious results from the single test site that did not align with the study results – in Taluma, Colombia – may be attributed to a number of factors that merit further research. N2O emissions there were by far the lowest at any test site and were the same on both degraded and healthy pastures. The cattle urine used in the experiment had the lowest nitrogen content compared to the other research sites, which likely contributed to the results. The forage grass used there, Brachiaria humidicola, also has an especially high nitrification inhibition capacity, meaning that it prevents nitrogen from becoming N2O.

Power of data from far-flung places

The study is a victory for well-designed, modest-budget science. The project began with a weeklong training session at CIAT headquarters in Cali, Colombia, where a team of Ph.D. students from the additional participating countries – Argentina, Brazil, Nicaragua and Trinidad and Tobago – helped design the research plan and standardized the study’s methodology.

The students returned to their home countries and carried out the experiment to coincide with their area’s rainy seasons, to assure similar climate conditions across study sites. (The exception was Taluma, which was sampled during a period characterized by low rainfall, which is also another possible reason why the N2O emissions were lower there).

“The power is in the number of data points from all the different countries,” said Chirinda.

Better cattle greenhouse gas estimates

Researchers said the study is a useful step toward creating a more detailed picture of the scope of greenhouse gas emissions from cattle farming in LAC.

“Since work on emissions from livestock in the region is not common, this study generates at least one piece of information that is missing from theoretical greenhouse gas estimates in the LAC region,” said Miguel Andrés Arango, a co-author and scientist at Colombia’s AGROSAVIA, the nation’s largest agriculture research organization.

“Being able to estimate the real impact of cattle production will allow us to propose potential practices for reducing emissions,” said Arango. “It is high time we know the emission factors for our agricultural systems.”

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Collaborators and funders

The study was conducted under the framework of the Latin America climate change Mitigation Network (LAMNET) and implemented as part of the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), which is carried out with support from CGIAR Fund Donors and through bilateral funding agreements. For details, please visit https://ccafs.cgiar.org/donors. Part of this work was also supported BBSRC project BBS/E/C/000I0320 awarded to Rothamsted Research.

Collaborators on this project included researchers affiliated with the following organizations: the National Autonomous University of Nicaragua; the National Institute of Agricultural Technology in Argentina (INTA); the Federal University of Rio Grande do Sul (UFRGS) and the Institute of Agriculture and Forestry Management and Certification (IMAFLORA) in Brazil; the University of the West Indies in Trinidad and Tobago; Universidad Nacional de Colombia; the United States Department of Agriculture (USDA); and the University of Vermont.

The International Center for Tropical Agriculture (CIAT) is a CGIAR research center. CIAT develops technologies, innovative methods and knowledge that enable farmers, especially smallholders, to make agriculture more competitive, profitable, sustainable and resilient. Headquartered in Cali, Colombia, CIAT conducts research for development in tropical regions of Latin America, Africa, and Asia. https://ciat.cgiar.org

World Agroforestry (ICRAF) is an autonomous, non-profit research organization whose vision is a rural transformation in the developing world as smallholder households increase their use of trees in agricultural landscapes to improve food security, nutrition, income, health, shelter, social cohesion, energy resources and environmental sustainability. The center generates science-based knowledge about the diverse roles that trees play in agricultural landscapes, and uses its research to advance policies and practices, and their implementation that benefit the poor and the environment. http://www.worldagroforestry.org

CGIAR is a global research partnership for a food-secure future. Its science is carried out by 15 research centers in collaboration with hundreds of partners across the globe. https://www.cgiar.org

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http://dx.doi.org/10.1038/s41598-018-37453-2

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