Only a fraction of conventional row crop farmers grow cover crops after harvest, but a new global analysis from the University of Illinois shows the practice can boost soil microbial abundance by 27%.
The result adds to cover crops’ reputation for nitrogen loss reduction, weed suppression, erosion control, and more. Although soil microbial abundance is less easily observed, it is a hugely important metric in estimating soil health.
“A lot of ecological services are done by the soil microbiome, including nutrient cycling. It’s really important to understand how it functions and how agriculture can form a healthier soil microbiome,” says Nakian Kim, doctoral student in the Department of Crop Sciences at the University of Illinois and lead author on a new paper in Soil Biology and Biochemistry.
Other studies have shown benefits of cover cropping on the soil microbial community, but most of them have been one-offs influenced by specific site conditions, unique seasonal effects, idiosyncratic management regimes, and the researchers’ chosen analysis methods. Kim’s work is different in that he looked for universal patterns among dozens of these one-off studies.
“Our analysis shows that across 60 field studies, there was a consistent 27% increase in microbial abundance in fields with cover crops versus no cover crops. It’s across all these studies from around the world,” says Maria Villamil, associate professor in crop sciences and co-author on the paper.
The research team performed a search of the existing studies on cover crops, and wound up with some 985 scientific articles. Of these, they only kept studies that directly compared cover crops and bare fallow soils, and omitted studies conducted in greenhouses or that treated crop residues as cover crops. They also ensured that the studies were statistically sound, with reasonably large sample sizes. In the end, they mined and reanalyzed data from 60 studies reporting on 13 soil microbial parameters.
“That’s why the criteria of selection had to be so strict. We wanted to compare studies that were solid, and with enough replications that we could make valid claims about global patterns,” Villamil says.
“For me, it was surprising to see the consistent, positive effect of cover crops — surprising but good. Finally! … the microbiome, that’s where it’s at. That’s how everything is related. Thanks to this work, I have something to look forward to when I put in cover crops, and have generated many more questions in need of research,” Villamil remarks.
