Thanks to Dennis O’Brien and researchers at the USDA Agricultural Research Service for their assistance on this article.
Decades of plowing throughout the Piedmont region of the United States have degraded the soil, allowing much of it to be washed away, and robbing what is left of nutrients and organic matter. Sorghum, cotton, soybean, and wheat are still widely grown in the region, which stretches all the way from Alabama to New Jersey. But because the soil is so degraded, growers have allowed much of the land to revert to forests and pastures.
But is that the best way to improve the soil? That’s the question that Alan Franzluebbers an a Agricultural Research Service Ecologist decided to address: “Growers need guidance on whether leaving the land unused is the best way to restore degraded soils or whether allowing cattle to graze on it is a viable option.”
Franzluebbers led a twelve-year assessment of how soils would respond to different kinds of fertilizer and different grazing scenarios on 37 acres of rolling, eroded land in northeastern Georgia. They planted coastal bermudagrass and drilled in tall fescue 5 years later to extend the grazing season from 5 months to 10 months. They looked at the effects on the soil and on forage growth of three different fertilizer treatments (inorganic fertilizer alone, organic broiler litter alone, and a mix of inorganic fertilizer and organic broiler litter). To that they added 4 different management 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 haying on ungrazed pasture.
The team found that fertilizer type made little difference. It was simply important to supply nutrients to meet the demand of growing forage for grazing. But how forage was used did make an impact on the development of soil properties. When forage was hayed continuously, surface residue was low, soil bulk density was high (translating to more compaction), and soil organic matter remained relatively unchanged. When forage was grazed by cattle, surface residue was low to moderate, soil bulk density was low to moderate, and soil organic matter increased.
When forage wasn’t grazed (similar to a Conservation Reserve Program management scheme), surface residue was highest, soil bulk density was low (similar to low grazing pressure), and soil organic matter was intermediate between haying and grazing. Land that was grazed produced more grass than land that was hayed and grazing led to the most carbon and nitrogen being sequestered in soil with low grazing pressure providing slightly better results than high intensity grazing.
In the end, the team discovered that the idea that grazing is worse than leaving the land unused if false. If producers manage cattle so that pastures are grazed moderately, they’re actually restoring soil quality.