by Courtney Llewellyn
Farmers all are too familiar with what’s left over after harvest – the corn stubble that pokes up through the snow all winter. It may not seem useful, but corn residue can actually be a valuable resource. The leaves, husks, kernels and cobs can serve as food to grazing cattle. And, when properly managed, corn residue can increase farm income, provide affordable food for cattle and efficiently use land to feed people.
The interactions of cattle grazing and crop productivity are studied by Morgan Grabau, a graduate research assistant at the University of Nebraska-Lincoln and a member of the American Society of Agronomy. “Corn residue is an under-used resource. Only 15% of the corn residue acres in the central U.S. are grazed,” she said. “Cattle turn this cheap, abundant feed resource into quality beef.”
She added that grazing livestock can help increase soil health and fertility by recycling nutrients back into the soil and increasing microbial populations which help with residue breakdown. If producers supplement cattle while grazing residue, nutrients can be imported into the field. She said this has been seen with the mineral phosphorus.
But crop producers can worry that cattle trampling could still negatively affect soil physical properties and subsequent crop yields. Research conducted at UNL has shown that grazing corn residue at the recommended stocking rate does not reduce corn or soybean yields the following growing season. A long-term study in Mead, NE, showed improvements of two to three bushels/acre in soybean production following grazed corn residue when managed in a corn-soybean rotation. The result was the same whether cattle grazed in autumn (November – January) or spring (February – April).
The Western Corn Belt Region is where most corn residue is grazed after harvest, with Colorado, Nebraska, Kansas and South Dakota having greater than 20% utilization rates. The Northeast and Eastern Corn Belt Region have the lowest utilization rates (less than 5%), which is likely due to fewer cattle and perhaps insufficient knowledge that corn residue can be used as a forage resource, according to Grabau.
Approximately 45% to 50% of aboveground biomass produced by corn plants is residue – so corn production of 150 bushels/acre produces about three tons/acre of residue. Of this residue, about 40% (or 16 pounds/bushel) is leaf and husk, which are highly digestible and good sources of cattle feed. Cattle will also eat any grain remaining first, which reduces the likelihood of volunteer corn.
It’s been proven that residue protects soil from erosion, and so some cornfields, because of their topography and/or low corn grain yield, should not be grazed. “There is not a particular farm size that is more often used for grazing residue. It is more important to be cognizant of sites that are more high risk for erosion, such as hilly expanses and anywhere with a slope,” Grabau explained. “Erosion on slopes can be prevented with ground cover, so producers can keep an eye on these areas. Since cattle do not necessarily graze in an even distribution, it is also important to watch for areas being overgrazed.”
Producers can still turn cattle back out in the early spring, if there is a weather event (snow or ice) that prevents cattle from grazing in the fall/winter, she added. “Grazing residue in the spring means grazing in the months of February and March, which allows for cattle to consume forage while the forages out on pasture have not greened up yet and are not actively growing. Additionally, using that residue in the spring as a feed source lowers feed costs and reduces producers’ reliance on hay and other stored feedstuffs, all the while with no major long-term impacts on the soil.”
Stocking densities are determined based on 50% utilization of the leaf and husk (eight pounds/bushel), or about 20% of the residue. A table of recommended stocking rates on corn residue is available at https://tinyurl.com/2wak9lef.
Grabau studied two different grazing systems. In one, researchers let a small number of cattle graze cornfields for 45 days starting in mid-February. The other system tripled the number of cattle but cut grazing time to just 15 days in March – so the total amount of grazing was equal. The time spent on wet fields varied, which could affect how the soil responds to all that trampling.
The team measured various soil properties that contribute to compaction and the yield of the soybeans planted in the fields the following season after cattle were done grazing. The team repeated the experiment over two years.
Compaction is measured in two different ways: bulk density and soil penetration resistance. Bulk density is the true measure of compaction, which looks at porosity (how close the soil particles are together). Penetration resistance is a simulation of root growth in order to measure how easily roots can penetrate through the soil due to compaction, Grabau explained. Water content can influence compaction. After a precipitation event, farmers may be encouraged to wait a day or two prior to entering a field. “However, we did the exact opposite with this study,” she said. “Even when we created a worst-case scenario, grazing in the spring when the ground was wet, compaction was minimal and subsequent soybean yields were not negatively affected. Thus, compaction should not be a reason for not grazing corn residue.”
Soil organic matter influences compaction because less organic matter means less structure, potentially leading to increased compaction, or at least the soil has less resistance/resilience to compaction. Soil texture is another important property, as clay soils are more easily compacted than sandy soils. And soil aggregates contribute to the stability and structure of the soil. With poor aggregation, the soil is more susceptible to degradation and compaction, Grabau explained.
“Much like previous fall grazing studies, minimal effects were seen on soil properties and yield due to spring grazing, regardless of the number of cattle and area grazed,” she said. The soybean productivity of the fields following grazing did show some changes. The highly concentrated 15-day grazing actually increased yields slightly. “This yield increase could be due to more residue removed, causing warmer soil temperatures for plants to grow,” Grabau said.
While cattle do cause some soil compaction, the effects are limited to the surface level of fields. “Compaction isn’t permanent,” Grabau said. “Soil can loosen up again as it dries and saturates over and over, and microbial activity in the soil also reduces compaction.”
Although autumn and winter grazing is probably still the best solution, Grabau said farmers shouldn’t be afraid of grazing cattle in the spring.
“The integration of crops and livestock is a beneficial production system,” said Grabau. “Grazing cattle on corn residue can be a great way to make even more food for human consumption from corn fields, as both the corn grain and plant residue can be used as feed for livestock.”