PLANTING cover crops in rotation between cash crops — a practice widely agreed to be ecologically beneficial — is even more valuable than previously thought, according to a team of agronomists, entomologists, agroecologists, horticulturists and biogeochemists from Pennsylvania State University's College of Agricultural Sciences.
"As society places increasing demands on agricultural land beyond food production to include ecosystem services, we needed a new way to evaluate 'success' in agriculture," Jason Kaye, professor of biogeochemistry, said. "This research presents a framework for considering a suite of ecosystem services that could be derived from agricultural land and how cover crops affect that suite of services.
"Cover cropping is one of the most rapidly growing soil and water conservation strategies in the Chesapeake Bay region and one we are really counting on for future improvements in water quality in the bay. Our analysis shows how the effort to improve water quality with cover crops will affect other ecosystem services that we expect from agricultural land," Kaye said.
The team's research, published in the March issue of Agricultural Systems, quantified the benefits cover crops offer across more than 10 ecosystem services, including increased amounts of carbon and nitrogen in soils, erosion prevention, more mycorrhizal colonization — a beneficial soil fungus that helps plants absorb nutrients — and weed suppression.
Lead researcher Meagan Schipanski explained that commonly used measurements of ecosystem services can be misleading due to the episodic nature of some services and the time sensitivity of management windows.
"For example, nutrient retention benefits occur primarily during cover crop growth, weed suppression benefits occur during cash crop growth through a cover crop legacy effect and soil carbon benefits accrue slowly over decades," she said. "By integrating a suite of ecosystem services into a unified analytical framework, we highlighted the potential for cover crops to influence a wide array of ecosystem services. We estimated that cover crops increased eight of 11 ecosystem services. In addition, we demonstrated the importance of considering temporal dynamics when assessing management system effects on ecosystem services."
Trade-offs occurred between economic metrics and environmental benefits, Schipanski said. She noted that planting cover crops will become more attractive if fertilizer prices rise or if modest cost-sharing programs like one currently in place in Maryland are developed.
The researchers simulated a three-year soybean/wheat/corn rotation with and without cover crops in central Pennsylvania using agroecological conditions broadly representative of the Northeast and mid-Atlantic regions. The cover crop rotation included red clover that was frost-seeded into winter wheat in March and winter rye that was planted after corn was harvested in the fall.
The research, funded by the U.S. Department of Agriculture, used simulated management practices, including tillage, synthetic fertilizer use and mechanical weed control.
The planting of cover crops already is accepted as an environmentally prudent practice. It is so beneficial, in fact, that the Natural Resources Conservation Service (NRCS) last month set a goal to increase the area planted nationally to cover crops from the current 2 million acres to 20 million by 2020.
According to NRCS, in 2006, only 5% of cropped acres in the Chesapeake Bay region had cover crops planted every year, and 88% of acres never had any cover crops planted. In 2011, 52% of acres had cover crops planted at least once every four years, and 18% of acres had cover crops planted every year.
NRCS estimated that the increased annual use of cover crops in 2011 led to an average 78% reduction in sediment loss, 35% less nitrogen surface loss, 40% less nitrogen subsurface loss and 30% less total phosphorus loss.
However, many farmers have not planted cover crops because they have not had a financial incentive to do so, according to Kaye. This, he said, is largely because the traditional method of calculating the economic value of cover crops — estimating only the resulting increase to cash crop yields over a short period — was not compelling to producers.
"The most common metrics for evaluating cropping systems are grain and forage yields and short-term profitability," he said. "Within this context, cover crops are treated as a tool to be used only if they do not interfere with cash crop production."