Good News About Ground Covers for Organic Gardeners

Conventional and organic farmers know that plastic or fabric ground covers can help suppress weeds and retain soil moisture. But using these ground covers as a chemical-free weed control can be complicated for organic farmers who need to till composted manure into their crop fields after planting.

Agricultural Research Service soil scientist Larry Zibilske, who works at the Integrated Farming and Natural Resources Research Unit in Weslaco, Texas, set out to see how these ground covers limit water penetration and affect carbon and nutrient levels in soils. He conducted a soil chamber study using two types of commercial ground covers: One was a needle-punched, double-layer fabric, and the other was a tightly woven material made of flat polypropylene strands. Two types of compost—poultry litter pellets or a compost mix of cattle manure and other organic materials—were used in the research.

Zibilske monitored the movement of nutrients from the two types of composted materials through the two types of ground covers for 30 days. Water was able to pass freely through the fabric cover, but the polypropylene cover limited the movement of water for the first 2 weeks. However, water was able to pass through the polypropylene cover much more easily by the end of the study, perhaps because the cover was becoming coated with organic molecules from the compost.

Levels of beta-glucosidaseare sometimes used as a soil quality index to assess how the influx of soluble carbon affects soil microbial activity. Zibilske found that beta-glucosidaselevels were essentially the same in soils protected by fabric covers, soils protected by polypropylene covers, and control soil samples without a ground cover. This similarity suggests that these ground covers did not significantly alter or limit biological activities in the soil.

But Zibilske did note links between fabric covers and reduced soil levels of carbon and nutrients. For instance, soil covered by fabric contained only 84 percent of the carbon that the control sample contained, and the soil protected by the polypropylene material contained only 80 percent as much of the carbon as the control sample. Soil samples from the covered columns also had somewhat lower nitrogen and phosphorus levels than the controls.

These results, which were published in 2010 in the International Journal of Fruit Science, show that some organic farmers who need to periodically amend their soils with composts after planting can still control weeds—and costs—by using fabric ground covers.—By Ann Perry, Agricultural Research Service Information Staff.

Larry Zibilske is in the USDA-ARS Integrated Farming and Natural Resources Research Unit, 2413 E. Highway 83, Weslaco, TX 78596-8344; (956) 969-4832.

"Good News About Ground Covers for Organic Gardeners" was published in the August 2011 issue of Agricultural Research magazine.