Value of soil: Experts explain importance of soil healthWritten by Gayle Smith
Boelus, Neb. – When it rains several inches and a field is vacant of plant life, how much water infiltrates into the soil? During a recent cover crop field tour in Boelus, Neb., soil experts addressed this question.
“Soil health is the capacity of the soil to function as a vital, living ecosystem to sustain plants, animals and humans,” explains Linda Schott, University of Nebraska-Lincoln an Extension assistant at UNL. “It is made up of physical, biological and chemical properties that all interact.
According to Aaron Hird, Natural Resources Conservation Service (NRCS) soil health specialist, producers need to find better ways to infiltrate water into the soil.
“If the soil can only infiltrate water at one-half inches to one inch an hour, it's a problem because we get bigger rains than that,” he explained. “We don’t have a soil erosion problem in most areas, we have a water infiltration problem.”
“We have to find better ways to get that water into the ground and not have it run off. We build soil by adding to it. It builds from the top down,” he said.
Benefits of plants
Hird said he likes to see a field with living roots at least 10 months out of the year to give the ecosystem an opportunity to build relationships.
“Soil biology for plants and animals is dependent on plants providing food,” he explained.
If a field is bare from October until March, there is nothing feeding the food microorganisms in the soil, so they die and disappear. Earthworms are one of the easier species to identify, but there are many other species that depend upon plants to provide nutrients.
When cover crops are grazed, the plant loses the same amount of root mass as what is grazed off.
“If we graze half, half of the root system dies,” Hird explained. “When we leave half, it helps the roots rebuild in the soil. When the roots die, all that organic matter stays there, and the plant can regrow.”
“Basically, we are dumping the root structure into the soil and re-growing it. It makes us twice our money by having cover crops. Grazing and re-growing is a critical opportunity,” he noted.
Carbon is also important to soil health.
Paul Jasa, Extension engineer with UNL, explained, “If we go into a field that has been tilled forever and expect to see carbon building in the soil, we will be very disappointed. The bioactivity of the microbes isn’t there to cycle the nutrients and roots out of the residues. A lot of people think if they plant a cover crop one year, it will change that, but their soil is no different.”
“We can’t take a root and change the soil in one year. It takes several,” Jasa continued.
Research has shown that producers can only expect a 0.5 percent change each year in a long-term system to establish a new dynamic. However, that dynamic can be sped up with the combination of cover crops and livestock grazing to increase the carbons and microbes in the soil.
“The bacteria in the rumen is similar to the bacteria in the soil that cycles the residue and builds organic materials there,” Jasa explained.
Greg Rasmussen has a field of cover crop mixture north of Boelus, Neb.. Before he purchased the land in 2013, it had been in a corn and soybean rotation.
“When I purchased it, the renters mentioned that there were some severe slopes and hills throughout the field,” he said. “The erosion was bad enough that they were farming around the washouts. After I purchased it, we did some waterway work to curb some of the erosion.”
In 2014, Rasmussen said he planted oats in the field in March, terminated the oats and planted soybeans.
“We had a really good soybean crop, and we planted wheat into the soybean residue. The wheat winterkilled, so we came back in with a spring grazing mix and grazed it,” Rasmussen explained. “Last fall, we planted another grazing mix and followed that with rye, which we killed this spring and replaced with oats.”
“The oats yielded nearly 80 bushels per acre,” he said. “We planted another grazing mix and will graze that this month.”
Learning from cover crops
Rasmussen said he has learned a lot from growing and grazing cover crops.
“The biggest thing I’ve learned is not to leave the cattle on it too long,” he commented. “If we let them eat more than half of it, it slows the regrowth. The first year we farmed this field, there were two years of cornstalks here because they had no-tilled.”
He continued, “What I have noticed since then is my organic residue is breaking down a lot faster now, and compaction is less. I can tell when I am using equipment that the soil isn’t as hard. We use a John Deere no-till drill. We have had to back the hydraulic pressure off and lessen the depth settings.”
Rasmussen has also learned the importance of grazing cover crops at the optimal time.
“Last year I had a grazing mixture sampled at Ward Laboratories for nitrates. When I called for the results, I found out this mix wasn’t only good grazing but exceptional grazing,” he said. “Grazing time is important. If we wait too long to graze, it gets tall and stalky, and they leave a lot behind. If we graze it more timely, the cattle will just take the tops off, which lets regrowth occur. It is not only good for the cattle but for soil health.”
Mary Drewnowski, beef systems engineer with UNL, told producers they may not get a ton of regrowth on the warm season plants, like sorghum Sudan, in the fall, but if oats are planted with it, they will take off with a little bit of rain. Sorghum-Sudan and sunflowers are warm season grasses that go through their rapid growth phase in June and July.
“If we graze in mid-October, there will be no regrowth, so we could graze it as much as possible while still maintaining adequate ground cover,” she said.