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Montana State University professor discusses effect of cover crops on soil quality

BOZEMAN, Mont. — In this year’s Provost’s Distinguished Lecturer Series at Montana State University, Catherine Zabinski, a professor in the Montana State University’s Land Resources and Environmental Science Department in the College of Agriculture, discussed the aspects of plant life, and the relevance for natural and managed plant communities.

The lecture, “Roots and microbes: The world beneath our feet,” was held April 12 at the Museum of the Rockies’ Hager Auditorium.

As part of her lecture, Zabinski highlighted a study that began in 2012 with researching the physical, chemical and biological effects of mixed cover crops on soil quality. This study takes place in the Golden Triangle, between Havre, Conrad and Great Falls, Mont. The Golden Triangle is known for its excellent wheat-growing conditions.

“There has been interest from farmers for a while in the potential to grow cover crops for the beneficial impacts on soil quality to increase nitrogen and reduce water use,” Zabinski says.

One part of the study focuses on the relationship between plants and the microbes that primarily live in plant root systems. By looking at mycorrhizal fungi that form a mutually beneficial relationship with the plant host, Zabinski and her team hope to better understand the implications different cover crops might have on soil health and fertility.

Looking at wheat systems, Montana farmers have alternated wheat with fallow, because keeping the fields open for a year potentially increases the water storage so the subsequent year will yield a more productive wheat crop.

“In Montana, we can document that there are positive impacts on soil quality parameters after growing cover crop mixtures relative to single species or fallow,” Zabinksi says.

The study, which was funded by the U.S. Department of Agriculture Western SARE Program, divided crop species into four functional groups: nitrogen fixers for fertility impacts, fibrous rooted plants to add carbon to the soil, tap-rooted plants that break up hard pans in the soil, and brassicas to create surface cover and potentially reduce weed impacts.

“We, in fact, know that plants have their own microbiome, and it’s a different set of bacterial communities that exist on the leaves than in the seeds, flowers and roots,” Zabinski says. “We’re just barely scratching the surface. Using molecular tools we can talk about the composition of the communities they’re in, and understand that roots have a lot of influence in terms of biomass and carbon fixes.”

Clain Jones, an MSU Soil Fertility Extension specialist, worked on the project with Zabinski and says, while there are few biological differences in soil quality when using single versus multi-species cover crops, there is almost always differences when practicing cover crops instead of fallow. And despite the benefits and improvements in soil quality, producers may still face challenges.

“From an economic perspective, in the short-term there is disincentive, because using cover crops cost money and managing,” Jones says. “There’s also the cost of the cover crops using water. So, we’ve generally found that the subsequent wheat crop yield is generally lower after cover crops, but sometimes we’ve found higher protein levels. In the short-term perspective, cover crops don’t have a chance of paying.”

But, Jones has reason to believe there are long-term incentives to using cover crops. In other long-term studies, such as one led by MSU Professor Perry Miller, research has shown impressive increases in nitrogen and protein in later years.

“For the grower who is thinking long-term about passing on better land and better soil, cover crops are a better incentive,” says Jones, who has found it takes eight to 10 years to see economic benefit. “It’s like banking soil quality to increase financial return in the future.”

The study will continue for the next five to seven years at two of the four sites and will look further into grazing systems. The team will pull samples from the last two sites this spring and aims to publish the results at the beginning of the summer.

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