Cover crops, often planted in effort to control erosion, tie up nutrients, improve soil quality or suppress weeds, have grown in popularity recently. But understanding the crops' true value for cash crops grown on the same soil – and ecosystems around the field – has been difficult.
With new research published in the March issue of the Agricultural Systems journal, a group of agronomists, entomologists, agroecologists, horticulturists and biogeochemists from Penn State's College of Agricultural Sciences aimed to quantify the real value of cover crops.
"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," said Jason Kaye, professor of biogeochemistry.
"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," he said.
Cover cropping is a popular conservation strategy in the Chesapeake Bay region, largely an effort to improve water quality.
"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 added.
Stacking up the benefits
The research quantified the benefits offered by cover crops across 11 ecosystem services. Benefits included increased carbon and nitrogen in soils, erosion prevention, more beneficial soil fungi that help plants absorb nutrients, and weed suppression.
Lead researcher Meagan Schipanski explained that commonly used measurements of ecosystem services can be misleading due to the sporadic nature and timing of some services cover crops provide.
For example, cover crops' ability to retain nutrients happens primarily during the growth stage. Weed suppression, however, occurs during growth of the cash crop. Soil carbon benefits occur slowly over decades.
By mixing all the services into one analytical framework, Schipanski says the research revealed how cover crops influence each one.
"We estimated that cover crops increased eight of 11 ecosystem services," she said. They also demonstrated the importance of timing when evaluating management system effects on ecosystem services.
Trade-offs occurred between economic metrics and environmental benefits, Schipanski said. She noted that the planting of cover crops will become more attractive if fertilizer prices rise or if additional modest cost-sharing programs are developed.
A broader look
Researchers simulated a three-year, soybean-wheat-corn rotation with and without cover crops in central Pennsylvania, which presented conditions broadly representative of the Northeast and mid-Atlantic regions.
The cover crop rotation included red clover, frost-seeded into winter wheat in March, and winter rye, planted after corn was harvested in the fall.
The study also used simulated management practices, including tillage, synthetic fertilizer use and mechanical weed control.
The study is particularly timely as the National Resource Conservation Service just last month set a goal to increase the acres planted nationally in cover crops from the current two million 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.
The 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, a 40% cut in nitrogen subsurface loss, and a 30% decrease in total phosphorus loss.
But many farmers have not planted cover crops because they have not seen financial incentives to do so, according to Kaye. That is largely because the traditional method of calculating the economic value of cover crops used by agricultural producers -- only estimating the resulting increase to cash-crop yields over a short period -- was not compelling.
"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."
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Source: Penn State