While the short-term effects of grazing crop residue appear minimal or even beneficial, questions remain regarding longer-term effects of grazing on soil compaction, structural quality, organic-matter content and nutrient cycling.
To address those questions, 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.
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 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 benefiting soil organic material.
The researchers conclude, for this study, long-term corn-stubble grazing does not negatively affect soil structure, organic matter content or subsequent crop yields.
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