North Carolina State University soil scientists have received $700,000 from the U.S. Department of Agriculture (USDA) to examine how winter cover crops on organic farms can make the soil healthier to help organic farming meet increased demand from consumers.
The funding from the USDA's National Institute of Food and Agriculture will help NC State scientists evaluate the important role legume cover crops – inedible varieties of peas like hairy vetch and Austrian winter peas, as well as plants like crimson clover – can play in sucking carbon out of the air and sequestering it in the soil, says Dr. Julie Grossman, assistant professor of soil science at NC State and the primary investigator on the project. The unique ability of legumes to remove nitrogen from the air and use it as a plant nutrient is well known, but the role of legumes in capturing carbon in the soil is far less understood, she adds.
The NC State team will study soils used in, or transitioning to, organic production – an ever-growing amount of acreage each year.
Cover crops are planted at times when cash crops are not in the ground, frequently in the winter, Grossman says. They are important because they provide a number of environmental benefits, such as controlling erosion, providing soil nutrients and organic matter, and reducing pests. These benefits are especially important in organic production, which by definition precludes the use of synthetic fertilizers and pesticides.
Because of its restrictions on using synthetic herbicides for weed control, organic farming often uses tillage, or raking and turning over the soil, to control weeds and kill cover crops before cash-crop planting. Tillage, however, releases lots of soil carbon into the atmosphere. Like trees and oceans, soil is a powerful "carbon sink" – it holds four times as
much carbon as there is in plants and animals and three times as much carbon as there is in the atmosphere, Grossman says. Replenishing carbon in the soil can make organic farming a more carbon-neutral process, which is an important climate-change consideration.
"We are concerned with the health and sustainability of the soil – you will often hear organic farmers use the motto 'Feed the soil, not just the plant,'" Grossman says. "Organic farming has been shown to be extremely beneficial to the soil; our goal is to understand exactly how and to properly manage what we learn."
The study will examine which cover crops are more effective in capturing atmospheric carbon and placing it in the soil, and how the different cover crops interact with tiny soil microbes that aid the process. It will also compare different methods of killing the cover crop before cash-crop planting – like rolling or mowing the cover crops as opposed to tillage – and how these techniques affect soil carbon levels.
The funding will help train graduate students to improve ways of educating farmers about the research and its findings. It will also be used to set up a series of online workshops to educate an even wider audience.
NC State's Department of Soil Science is part of the university's College of Agriculture and Life Sciences.