Moderate grazing can restore degraded soils and reduce carbon dioxide emissions, say USDA-ARS researchers.
They gave growers in the Piedmont, which stretches from Alabama to Virginia, guidance on how to make their land productive again. Cotton, soybeans, sorghum and wheat are widely grown there. But decades of plowing have degraded the soil and growers have slowly allowed much of the land to revert to forests and pastures, says Alan Franzluebbers, an ARS ecologist at the J. Phil Campbell Sr. Natural Resource Conservation Center in Watkinsville, GA.
He led a project where grasses were planted on 37 acres of rolling, eroded land in northeastern Georgia and pastures were grazed by beef cattle for 12 years to assess grazing effects on soil quality. Coastal bermudagrass was planted initially. After five years, tall fescue was drilled into the bermudagrass to extend the grazing season from five months to 10 months of the year.
The researchers varied the number of cattle per acre and assessed how the soils responded to four grazing scenarios: moderate grazing (average of 23 steers for every 10 acres), intensive or heavy grazing (35 steers per 10 acres), no grazing and letting the grass grow, and no grazing but cutting the grass for hay. Under each scenario, they looked at the amount of soil compaction that occurred, the amounts of organic carbon and nitrogen in the soil, and the amount of surface plant residues, which help prevent erosion. They also looked at how the soil responded to three fertilizer treatments (inorganic fertilizer alone, organic broiler litter alone and a mix of inorganic fertilizer and organic broiler litter).
The researchers found that, while fertilizer type made little difference, different grazing scenarios produced different effects, and the grazed land produced more grass than the ungrazed land and had the greatest amount of carbon and nitrogen sequestered in soil. Whether grass was grazed moderately or intensely made little difference on sequestration rates.
Cutting grass for hay reduced the amount of surface residue and increased soil compaction but didn’t change the amounts of organic carbon and nitrogen in the soil. Land left unused had the highest surface residue and least soil compaction and was better at sequestering carbon in the soil than haying.