Beginning in 1999, two locations in Iowa (Chariton, Atlantic) were used to study the effects of corn residue grazing by beef cows on soil characteristics and soybean yields the following growing season. Cows were allowed to graze inside selected paddocks at monthly periods throughout the fall and winter. For a grazed and ungrazed comparison, grazing exclosures were used inside the grazed paddocks, while one paddock was left ungrazed for a control. Also, the following year, equal portions of the fields went to no-tillage and disked soil prior to soybean planting so that effects of corn residue grazing on tillage treatments could be compared. The use of this design was to determine whether grazing had adverse effects on soil characteristics and, if so, at what date and weather conditions they occurred. Soil was analyzed for soil bulk density, moisture, penetration resistance, roughness, texture, and type. Corn crop residues were collected for yield, cover, and composition. Precipitation and soil temperature also were recorded throughout the grazing season. The following year, soybeans were harvested using a combine equipped with a yield monitor and global positioning system (GPS).
After two years of study at both locations, some grazing fields with corn crop residue have shown effects on soil and crop residue characteristics. Organic matter (OM) yield of crop residue generally decreases at the faster rate in grazed fields than organic matter of ungrazed fields. However, corn crop residue composition was the same in grazed and ungrazed fields except for the 1999-2000 season at Chariton where crude protein decreased but acid detergent insoluble nitrogen (ADIN) increased with no difference in fiber content between grazed and ungrazed paddocks. Corn crop residue cover and soil roughness both can be greatly affected by the interaction of grazing and weather conditions. When the temperature is above freezing and precipitation is adequate, cattle traffic can cause roughness, while reducing residue cover by working it into the soil. Even though grazing corn residue by cattle can increase the surface roughness, it has not yet caused any increase in bulk density measurements or any reduction in soybean yields. Penetration resistance ratios have shown some significant difference between grazed and ungrazed paddocks, but the reason is unclear.
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