Cover crops can add new life to S.C. soils
FLORENCE — “It’s alive!”
Though in this case, we’re not talking about the Frankenstein monster. We’re talking about soil.
Rather than being an inert medium, soil is a living ecosystem swarming with tiny creatures. But in many areas of the world, including parts of South Carolina, the soils may be alive but are feeling a bit… queasy?
Which is prompting farmers to search for ways to nurse their soils back to health.
Enter cover crops, which are plants placed into the soil to keep it covered when no cash crop is growing. In South Carolina, this is typically from October-November through April-May. Some warm-season cover crops also are used to blanket post-corn fields from August to November, then are with wheat.
Whether a lifesaver or just another option, the concept of using cover crops to improve soil health is a growing topic in South Carolina’s agricultural and research communities.
“What we’re seeing in South Carolina is a mirror image of what we’re seeing all across the country,” Buz Kloot, a research professor at the Arnold School of Public Health in the University of South Carolina, said during the recent SC AgriBiz & Farm Expo in Florence. “Farmers are saying, ‘Hey, there’s something going on here. We don’t know quite what it is, but we’re going to try.’ And scientists like me are saying, ‘We think this is what’s going on.’ And we’re scrambling to figure it out.”
In some circles, the growth and cost effectiveness of cover crops is up for debate. But the tangible need for healthier soils is not. Soil degradation and erosion are among soil’s worst enemies, reducing its effectiveness as a medium for any cash crop.
“Soil degradation is a symptom of soil being treated like an inert medium,” Kloot said. “Soils that are tilled and left uncovered, that have a growing root for less than half of the year, and that see no plant diversity will display these symptoms.”
For the most part, farmers combat this by applying fertilizers containing synthetic phosphorus, potassium, nitrogen and other expensive products. But when farmers seed their fields with cover crops such as rye, clovers, vetches, peas, radishes and sorghum, they are using plants to feed the soil microbes. A robust microbe population in turn increases the soil’s ability to recycle and supply nutrients to plants and also to store water. Multi-species cover crops add to the biological diversity of soils – and as diversity increases, the incidences of plant diseases and pests are reduced.
“Everything in the soil is dinner for everything else,” Kloot said. “As you introduce more species into the system, the tendency for one pest to become a problem is reduced because something else will prey on it.”
Typically, but not always, cover crops are terminated before reaching seed to avoid competition with any subsequent cash crop. One way of doing this is by using high-speed flail mowers and then tilling the residue into the soil. An emerging method, which is kinder to the soils, is the use of roller-crimpers, which roll the plants down and mechanically damage them by crimping them to form a weed-suppressing mat while simultaneously plugging cash-crop seeds through the mat and into the soil. Either way, much of the organic debris from the decaying cover crop is then ingested by the soil, which helps attract the beneficial microbes.
“The happier your microbes are, the more they will assist in recycling nutrients from plant material,” said Dara Park, an assistant professor at Clemson University who specializes in soil and water quality and who has been working in conjunction with Kloot on several ongoing projects. “In addition to microbes assisting with mineralization, organic acids released by decomposing cover crops promote chemical weathering of inert minerals in the soils. I think farmers are seeing effects from using cover crops that they haven’t seen before. A lot are saying, ‘I think I can cut back (on the amount of synthetic fertilizer).’ ”
David Robb, a graduate student in plant and environmental sciences at Clemson University, has been conducting a two-year study on vegetable production at the Clemson Student Organic Farm. In Fall 2013, Robb planted a cover-crop mix of cereal rye and crimson clover, which “overwintered.” In late spring 2014, he then “terminated” the cover crop in two different ways: On half the field, Robb used a mower and tiller; on the other half, he used a roller-crimper.
“I then divided both halves of the field into plots of summer squash and tomatoes,” Robb said. “The vegetable plots were further divided into rows receiving different levels of nitrogen fertilizer (100 percent, 50 percent and zero percent of the traditionally recommended amounts). I then recorded yield data for all crop/tillage/fertilizer combinations to compare the effects of tillage and fertilizer on vegetable production.”
In one season’s worth of data collection, Robb determined that the yields between the till and no-till methods were comparable. “However, when I factored in the labor, no-till produced significantly better results because it cost less than the tilled system,” Robb said.
Robb also found that altering the amount of fertilizer he used had no effect on his vegetable yields. The rows that received no fertilizer were as productive as the ones that received full amounts. “In general, agriculture suffers from a lack of cover cropping and is over-reliant on tillage and fertilizer inputs,” Robb surmised. “I’m hopeful that other farmers will experiment with no-till vegetable production using high biomass cover crops. I see it as win-win for farmers and for soil health.”