Research Explores Effects of Long-Term Residue Grazing

Even in the long-term, grazing appears to have no negative impacts on soil health or crop yields. 

Post-harvest corn residue provides groundcover and organic material, and also carries value as a low-cost feed source for cattle during the fall through spring. Several studies have shown little to no negative impact of grazing, at typical stocking rates, on subsequent crop yields. Less is known though, about the long-term effects of grazing on soil compaction, structural quality, organic-matter content or nutrient cycling.

Last week, we posted an article titled “Does residue grazing affect later crop yields?” This follow-up, also based on research from the University of Nebraska, looks at the longer-term effects of residue grazing on soil properties.

Nebraska researchers recently reported on a 16-year study, evaluating the effects of grazing on no-till, irrigated land in a corn-soybean rotation in eastern Nebraska. Their report, titled Effect of Long-Term Corn Residue Grazing on Soil Properties,” is published in the 2017 Nebraska Research Report.

The researchers compared three management systems:

• Fall grazing from November through January, with cattle stocked at 1.8 to 2.5 animal unit months (AUM) per acre.
• Spring grazing from February through mid-April, with cattle stocked at 2.3 to 3.1 AUM per acre.
• Control fields with no grazing.

In addition to yields, the researchers recorded soil cone index and bulk density as measures of compaction, soil organic matter, nutrients and wet aggregate stability.

Fall grazing in this study did not negatively affect any of the soil-structure characteristics relative to controls. Subsequent corn and soybean yields increased following fall grazing. The researchers note they designed the spring grazing program in this study to determine whether heavy stocking rates after the soil thawed would affect soil characteristics. They found that soil cone index increased somewhat following spring grazing, but remained below threshold levels where root growth could be restricted. Soil bulk density and wet aggregate stability were unaffected relative to controls. Soybean yields increased while corn yields were unaffected.

Spring or fall grazing had no significant effect on soil organic matter, although the researchers recorded a small numeric increase for both grazing systems compared with control plots.  The researchers note that grazing at normal stocking rates typically removes less than 25% of the crop residue, and cattle manure helps return significant volumes of organic material to the soil, especially if considering the additional manure nutrients resulting from supplemental feeds typically provided to cattle grazing corn residue. Also, the hoof action from grazing cattle could help incorporate residue into the soil, preventing photo-oxidation and thus benefitting soil organic material.

The researchers conclude that, under the conditions of this study, long-term corn-stubble grazing does not negatively affect soil structure, organic matter content or subsequent crop yields.

To help landowners determine appropriate stocking rates and grazing intervals on harvested corn fields, the University of Nebraska offers a Corn Stalk Grazing Calculator online.