September 13, 2012
Livestock producers can increase carbon sequestration and speed up soil-quality improvement in grazing areas by partially grazing cool-season forage during the growing season. That's one of the documented findings of a North Dakota Natural Resources Conservation Service (NRCS) grazing project designed to investigate how mid-season grazing of cover crops affects soil quality.
NRCS Burleigh County Conservationist Ken Miller says his office has conducted research for several years in regard to fall grazing cattle on warm season cover crops. For the 2011 season, researchers decided to add a growing season grazing element to their project.
"It wouldn't matter if it was sheep or cattle, the effects of grazing cool-season cover crops during the growing season would be the same," Miller says. "Regardless of the time of year, grazing activities result in trampled forage, which feeds soil biology. When plant residue is on the ground, it stimulates biological activity in the soil. Soil microbes recycle nutrients and enhance soil structure so water and air movement improves. They also reduce potential for disease and enhance plant growth. So adding this growing season grazing period means soil biology is more active over summer and soil quality improves at a faster rate."
Soil organisms continually transform nutrients in plant and animal residue to either organic or inorganic forms, creating plant-available nutrients that are stored in the soil. Decomposition of nutrients occurs more quickly during warm, moist conditions.
nt Livestock producers can increase carbon sequestration and speed up soil-quality improvement in grazing areas by partially grazing cool-season forage during the growing season.
Soil organisms also play an important role in formation of good soil structure. As soil temperatures climb during summer, soil fungi grow long filaments (hyphae) that surround soil particles and hold them together. Some soil bacteria produce sticky substances that aid in binding soil particles together.
The highest activity of soil organisms occurs during late spring/early summer and late summer/early fall. Grazing livestock during these periods provides soil organisms with both plant and animal nutrients necessary to active biological activity.
"Using sheep for the cool-season grazing also adds some diversity as far as livestock is concerned," Miller says. "We're striving for diversity in our crops. It's beneficial to add diversity to our use of livestock, too. The sheep do a fantastic job of trampling the forage. It's been fun to watch them move into a new paddock of triticale or vetch that's four to five feet tall. They go right through it and just lay it down on the ground."
For this grazing project, winter triticale and hairy vetch were planted in fall and grazed in spring. The sheep were brought in to graze about 50 percent of the forage. The sheep were then moved to a new area and a warm-season forage mix was planted into the remaining triticale and hairy vetch. Next a cool-season mix including flax, oats, wheat, forage peas, lentils, hunter turnip, Ethiopian cabbage, winter canola, annual rye grass, hairy vetch sweet clover and phacelia was grazed by the sheep. After grazing the cool season mix the sheep were moved to a field containing a warm-season mix of cowpea, soybean, turnip, radish, rice, sunflower, millet, sudan grass, sweet clover, grain sorghum, graza turnip, Ethiopian cabbage, black oats, buckwheat and safflower.
In the summer of 2012, approximately 120 dry ewes came in at the beginning of June to graze paddocks about one acre in size. The acre was grazed within a four to five day period, depending on the total amount of forage on each acre. Electric netting in combination with poly tape was used to form paddocks.
"Other than the forage, the sheep don't really need any kind of supplement," Miller says. "The forage provides all the necessary nutrients. However, the owner does provide a free-choice salt/mineral mix."
In 2011, the grazing project involved about 90 ewes. A central water point was set up in the 12-acre field where paddocks were created. By the end of the grazing season, it was evident that the sheep had created an area of compaction around the tank. They had also trampled some spots around the tank area to the degree that no forage was growing there.
"We ended up with some bare soil in the tank area," Miller says. "When we planted that field and recorded yield data, it was clear that yield was reduced in that area of compaction. So now we move the water tank every four to five days. Last year it sat in one place for a month.
"Any time you create compaction you do a tremendous disservice to soil biology," Miller adds. "Compacting soil presses pore spaces out of the soil, which greatly reduces soil biological activity. Eventually that degrades the level of organic matter. You always want to prevent compaction. It was easy to see where that compaction had occurred when we planted corn in that field. The yield was noticeably reduced."
Water does not easily penetrate compacted soils, which can result in reduced soil moisture content, soil loss through erosion, waterlogged soils in heavy rains that can drown plants, and anaerobic soil conditions where plant pathogens and diseases get a foothold.
Radishes, turnips, and annual rye grass are among the cover crops that help correct soil compaction. Deep rooting plants open channels through compacted layers to create open channels for air and water to penetrate compacted soil layers. When soil is properly aerated, there is improved moisture absorption, better moisture retention, better air and water movement deeper in the soil profile, and enhanced soil biology.
"In order to bring balance to soil quality, you need different types of plant roots to feed soil organisms," Miller says. "Through our research, we're seeing that there's a notable difference in crop quality when comparing areas where the sheep grazed and didn't graze. We've seen a tremendous response from corn planted on the acres the sheep have grazed. Getting that plant residue on the ground when it's warm and there's available moisture is making a significant difference in the balance of biological activity in our soils."