By Mary Drewnoski
One of the most common concerns about grazing corn residue is that cattle will cause soil compaction. A long term grazing data (16 years) conducted at the University of Nebraska has shown no compaction when grazing in the fall or the early spring. In this long-term study, grazing did not impact soil nutrient content. Which fits well with expected impacts given that cows in mid-pregnancy retain very little nitrogen, phosphorus or potassium. Thus, they excrete in manure and urine most of what they consume resulting in very little nutrients being removed from the land. With long term grazing there was an improvement in subsequent soybean and corn yields. This could have been due to the nutrient cycling being sped up as there is an increase in microbial biomass in the soil in the grazed areas.
More recently, a study was designed to test an extreme scenario for spring grazing. The thought was that if grazing was to cause compaction, it was most likely to happen when the soil is wet and thawed and when a high stocking density was used. The field was grazed at the recommended rate by starting in mid-February with 3 hd/ac for 45 days (normal stocking) or starting in early March with 9 hd/ac for 15 days (high stocking). Turn out of the higher stocking density groups was delayed until it rained to have the worst-case scenario. All groups were removed mid-March. There were some minor increases in bulk density (measure of compaction). The penetration resistance was also higher, and thus more down pressure had to be applied to get the soybeans planted. Down pressure applied at planting was 265 lbs in the non-grazed and 290 lbs in the grazed treatments. Much of the increase in penetration resistance is due to the soil having less cover and thus less surface soil moisture. The planting speed was also reduced due to the surface roughness. However, the subsequent soybean yields were still improved by grazing. While it is not recommended to graze late into the spring as this does have some downsides when it comes to planting, if cattle happen to be left out when a warm-wet spell occurs, there is no long-term damage to the land.
Source : unl.edu