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Sheep Grazing Builds Soil Health and Increases Microbial Activity on Vegetable Fields

Re-integrating livestock into cropping systems allows farmers to benefit from the natural synergism between plants and animals. These systems mimic nature and allow farmers to reduce the need for chemical fertilizer and tillage, improve soil health, and diversify farm income.

“Alpha diversity gives us a better definition of what we’re looking at.”
While most commonly practiced on a larger-scale, researchers at Montana State University (MSU) are looking into whether this beneficial management practice may also have an application in smaller-scale situations like vegetable farming. Funded by a grant from the Western Sustainable Agriculture Research and Education program, the on-going study is examining whether sheep grazing on vegetable fields can help improve soil health.

MSU research associate Devon Ragen is heading up the project, along with the assistance of graduate student Trestin Benson. A native of northwest Montana, Benson’s graduate research is seeking to understand whether grazing affects microbial diversity and subsequent crop yields in vegetable fields. Many past studies in row crop and small grain scenarios have shown livestock integration has a positive effect on soil health.

Sheep GrazingInitially, Benson says, the project was open to any kind of livestock. But given the timing and farmers who ended up participating in the study, it worked out sheep would be the best fit.

“They’re easy to manage, small, and portable,” says Benson. “They’re not like cattle where you have to put up a lot of fencing. For sheep, we just use electrified netting. It’s very easy to put up. Plus, two of the producers in the study already had sheep so they became the main livestock.”

The producers taking part in Benson’s trial include two local Montana operations, Strike Farms of Bozeman, MT and 13 Mile Lamb and Wool of Belgrade, MT, along with Black Cat Farms in Boulder, CO. Benson said it was easy to get the farmers involved because their participation doesn’t require them to change anything, just simply let her take soil samples before and after sheep are allowed to graze on each farm. It should be noted, sheep are either grazed before or after vegetable rows are planted or harvested.

“When we collect our soil samples we use a soil corer and just randomly pull 5 soil cores at a depth of 6 inches,” says Benson.

Additionally, Benson constructs 6 grazing exclosures at each site during each grazing period. Exclosures were randomly placed during year one. After last year’s grazing season, they were torn down and spot marked with a GPS for easy location the following season. The grazing itself is the treatment for the study, so the un-grazed areas (exclosures) are the control.

Bison GrazingAfter sample collection, soil cores are sent off to a lab where microbial DNA is extracted and analyzed to identify the species present and how and where they are clustering in the soil profile.

“We compared the different farms together and we can see that certain species are clustering on each particular farm,” says Benson. “So each farm has its own set of microbes unique to their soil, which is typical.”

Benson notes her preliminary results are mainly focused on looking at alpha diversity and species richness in the soil. Alpha diversity can be described as the richness and evenness of microbial species present.

“Saying just ‘biodiversity’ is ambiguous,” says Benson. “Alpha diversity gives us a better definition of what we’re looking at.”

To sample for the microbial diversity data Benson collected 5 soil samples from grazing exclosures and 5 soil samples from a designated grazed sampling area.

Preliminary results show significantly more alpha diversity and species richness of microbes on the grazed fields compared to before sheep set foot on each plot at the beginning of the study. This same result could be seen across all three farms.

“It was pretty awesome,” says Benson. “Essentially, it means the soil is becoming healthier!”

Along with increased microbial activity, Benson pointed out that compaction was a non-issue. In fact, results so far have shown that bulk density (an indicator of compaction) has actually decreased on all three farms since the start of the project.

Unfortunately, Benson says the opportunity to discover any differences in crop yields will have to wait.

Sheep Grazing“We have only collected one year of harvest so we don't have anything to compare to yet,” says Benson. “We just have a base of what happened this past summer. This fall we will get to collect the next harvest.”

Collaborating with National Center for Appropriate Technology, Benson shared her initial study results with the public at two workshop demonstrations earlier this year. She and her fellow researchers hope the study will encourage more producers to pursue incorporating livestock into smaller scale cropping systems like those used in the study.

Overall, Benson points out the most exciting result of this whole experience has been the huge uptick they’ve seen in microbial life after sheep were added into the vegetable farming equation.

“Even though we haven’t seen big differences between the grazed areas and ungrazed (exclosures) in each plot,” says Benson, “the fact that we saw a change in all three compared from before to after grazing, that's a huge deal.”

Going forward, Benson plans to look and compare data across years and see if she can tease out any indications of whether any particular microbial species are more prominent than others.