Cows, Carbon, and the Classroom

Cows, Carbon, and the Classroom

NAU looks at the relationship between grazing and changes in soil properties

by Jeremy D. Krones

L-R: Dr. Nancy Johnson, Joe Sweet, Judy Prosser, Aradhana Roberts, and Zach Sumner

Scientific research has been a part of the Diablo Trust since its inception, building on partnerships between the ranches and the various federal and state agencies to produce ecologically-informed management practices that are attuned to current scientific knowledge. Even after 24 years of work, not including the generations’ worth of experiential and anecdotal data gathered by the on-the-land managers, the work is not over. Every year there are new teams and students studying the ecology of the Bar T Bar and Flying M ranches.

Dr. Nancy Johnson, a professor in the School of Earth Sciences and Environmental Sustainability at Northern Arizona University (NAU), is following up on an experiment started over 18 years ago by NAU professor Dr. Tom Sisk. Along with undergraduate and graduate students, Dr. Johnson is examining the influence of grazing management practices on the amount of carbon and other elements in the soil.

Graduate student Aradhana Roberts recording her sample findings on the Bar T Bar

The Reed Lake experiment, located on the Flying M Ranch, compares three different grazing treatments repeated three times, for a total of nine one-hectare plots. Three plots are left unfenced to be the control group, or without any management that is different than the rest of the ranch. Three other plots are fenced to completely exclude livestock, and the remaining three are fenced to impose high-density, short-duration grazing. The third treatment is also called mob grazing; near the end of each summer, approximately 160 head of cattle intensively graze the plots for just 24 hours. Cattle are not allowed to graze those plots for the rest of the year.

Dr. Johnson was inspired to start this project after watching a TED Talk by Allan Savory, a well-respected but controversial wildlife ecologist from Rhodesia (now Zimbabwe). Savory is the founder of The Savory Institute and the developer of Holistic Resource Management (HRM). HRM is a unique approach to resource management, using an understanding of how the ecological, social, and economic components of a ranch and its community interact to create a more sustainable and productive ranching operation. A primary goal of HRM is to reverse desertification through carefully managed mob grazing, designed to mimic the grazing patterns of herds of native, hoofed grazing animals.

Allan Savory's TED Talk, "How to fight desertification and reverse climate change," February 2013.
[Photo from]


When Dr. Johnson saw Savory’s TED Talk, she said she was put off by what she saw as a lack of scientific backing to his claims, mainly about the ability of mob grazing to increase carbon stored in soil and reverse climate change.

“It just kind of sent me into this fact-finding mission, because I didn’t think he was saying things that made a lot of sense, based on what I know,” she said in reaction to the talk. “I felt that a lot of people who were saying this had absolutely no data to support it.”

In 2015, Dr. Johnson and Aradhana Roberts, one of her graduate students, found that the ranches around Flagstaff were ideally situated for them to study below-ground responses to above-ground management. Since the Flying M Ranch practices parts of the Savory Method, and Dr. Sisk’s plots had had continual treatments for over 18 years, Reed Lake was an appropriate place to start the research.

Ms. Roberts explained, “Another important intrigue in this project is the spectrum of responses that the literature is showing on grazing treatment and soil carbon. There are some that are showing increase, some showing decrease, and some showing no response. So, for sure there is a regional effect, but at the same time there is something greater happening with what grazing can offer to soil carbon.”

Ms. Roberts reported that they were able to get more data in just one year of studying the Reed Lake plots than many other studies, because of the longevity of the treatment and of how the project’s pastures are arranged. Ms. Roberts’ study of the Reed Lake plots showed that, as Savory predicted, mob grazing increased the amount of carbon in the top seven inches of the soil. The next step in the project is to determine the depth of this increased carbon, and calculate the capacity for this increased carbon storage to offset warming caused by the greenhouse effect.

Megan Deane McKenna, a master’s student with Dr. Johnson, will continue these studies at the Bar T Bar, where the soil has different properties. In addition to measuring soil carbon in grazed and un-grazed pastures she plans to examine ways to apply these findings to the carbon market. The carbon market is a market-based tool designed to limit greenhouse gas emissions from various industries through regulations and industry trading.

“Right now,” Ms. Deane McKenna said, “protocols are so complicated . . . they’re not being implemented.” The goal of her master’s thesis is to design better protocols so that those who work in the carbon market can more easily validate if there is carbon being stored, and what they can do about it.

Zach and Joe at an exclosure on the Bar T Bar Ranch by Interstate 40 in August 2016.


Two undergraduate students involved in this project are Zach Sumner and Joe Sweet, both in Environmental Studies. Mr. Sweet believes that since agriculture is such an important part of society and has impacts across the natural world, making it more sustainable will make it better for the natural ecology.

Mr. Sumner is also interested in sustainable agriculture, specifically in arid environments. He explained that for our region, "you couldn’t just set up a potato or corn farm and expect there to be enough water and get the same nutritional benefit you'd get from cattle."

This project has been a long time coming, and with each step the potential effects grow in the soil science, resource management, and agricultural worlds. Through research, collaboration between academic institutions and ranches, and an understanding of common goals, a more sustainable future for our ranches and shared resources is within our reach.