TWIN FALLS • Getting farmers to think about their soils as a living organism that needs to be fed just like livestock, rather than a medium for growing crops, is the first step toward healthy soil.
Marlon Winger, who is the state agronomist for the USDA Natural Resources Conservation Service, admits he didn’t use to pay much attention to the life under his feet. Sure, he took soil samples to make sure the plant’s nutritional needs were being met and he recognized that leaving crop residue on the soil surface helped reduce wind erosion.
But he didn’t really think about the microorganisms that teem through soil. At least not until he met Ray Archuletta, the NRCS guru on soil health, and began seeing what farmers in other parts of the country are doing to improve soil using cover crops. He’s convinced it will work just as well in Idaho.
The key is to keep a crop growing for as many days as possible during the year. Often, growers will harvest a bean crop and leave the field bare until the following spring when they disk or plow before planting.
Allowing a cover crop to grow for even as little as 30 days will benefit the soil, Winger told a small crowd during a break out session at Agri-Action. That’s because as plants photosynthesize and make polysaccharides (sugar), microorganisms in the soil are feeding off the polysaccharides. The longer the “bugs” can keep working, the more plant material they can convert to nitrogen, which will be available for subsequent crops.
As the bugs wiggle through the soil, they create macropores that allow water to infiltrate and loosen the soil so roots can go deeper. Microorganisms also exude compounds — Winger calls them “biological glue” — that bind soil particles together to form aggregates or clods that keep the topsoil from blowing away.
But the bugs can’t do that if they are starving. That’s why it’s so hard to increase soil organic matter in a wheat-fallow rotation. “You feed the system for four months and then starve it for eight months,” Winger said.
Even if you leave grain stubble standing after harvest and even irrigate it to encourage regrowth, you’re feeding the soil bugs you’ve got but you’re not increasing the population. Researchers are learning that the number of crops growing on top of the soil is directly related to the population and diversity of the microorganisms underground.
Growing a monoculture of wheat stubble above ground means just one microorganism is active below ground. But plant a cover crop mix consisting of three, or five, or even thirteen different species and suddenly there’s a whole metropolis of bugs at work.
Winger recognizes it is hard to get a cover crop growing in some situations, such as in corn stubble when irrigation water is limited or in fields that are surface irrigated. But he encourages growers to use cover crops whenever possible, and to treat the cost of seed just like the cost of any other input such as fertilizer or herbicide.
Reducing tillage passes will also help protect the soil ecosystems. “When it comes to building healthy soils, remember do not disturb,” Winger said.
Growers who are interested in adopting practices that improve soil health can apply for cost-share assistance through the NRCS Soil Health Initiative, a part of the Environmental Quality Incentive Program (EQIP). Farmers must apply by March 15 for 2013 funding. Stop by your local NRCS office for more details.
“It’s easy to see that cow herd is alive. You’ve got to feed them and haul water to them,” Winger said. “But you don’t think of the microscopic herd underground.”