LINDELL BEACH, B.C. — Cover crops have always been accepted as ecologically beneficial, but research is showing that they are far more valuable than previously thought.
Agro-ecologists, agronomists, horticulturalists, entomologists and bio-geochemists from Pennsylvania State University’s College of Agricultural Sciences have identified 11 “ecosystem services” provided by cover crops.
Together, they maintain soil health for not only successive cash crop production but also for beneficial insect and microbial communities.
Ecosystem services might not be a term that readily springs to mind when farmers talk about their fields, but they would identify with descriptions associated with cover crops such as food production, biomass production, nitrogen supply, nitrogen retention, soil carbon storage, erosion control, weed and pest suppression and beneficial insect conservation.
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“All farmers recognize that higher NO3 (nitrate) retention and nitrogen supply from cover crops can mean that more nitrogen gets to the cash crops,” said Jason Kaye, professor of biogeochemistry at Penn State.
“They would also recognize that weed suppression by cover crops could help with long-term weed pressure on the farm. Many farmers recognize that improved soil quality (such as increased carbon storage) and decreased erosion have long-term benefits for their farm. In contrast, I think there are only a few farmers who are actively thinking about N2O emissions, and I am not sure how many farmers are thinking about the role of beneficial insects in pest suppression on their farms.”
The study was conducted in the Chesapeake Bay region, where cover cropping has become a popular tool for soil and water conservation.
Researchers simulated a three-year soybean-wheat-corn rotation with and without cover crops. The covers were red clover frost-seeded into winter wheat and winter rye planted after corn was harvested in the fall.
Results, published in the journal Agricultural Systems, showed that improving water quality and retention through the use of cover crops had a substantial beneficial effect on all the other ecosystem services.
However, it comes with a cost.
“The clearest example is that cover crop seed and management cost money,” said Kaye.Â
“Some of those costs can be made up through reduced fertilizer costs if the cover crop is an N-fixing legume.”
He said some states in the Bay area have incentive programs that reimburse farmers for cover crops that prevent nutrients from leaving fields.
Short season cash crop varieties can lengthen the cover crop window, but may yield less.Â
On the plus side, cover crops can also be cash crops. They are good forages so they can be grazed in spring before a cash crop is planted and small grain cover crops can be left to mature and then harvested.
However, the opportunity to plant another cash crop after the main harvest will depend on local climate. It may be possible in the future to harvest cover crops as a biofuel feed stock before planting a cash crop.
The research also highlighted the fact that ecosystem services have time sensitivity.
“Nutrient retention benefits occur primarily during cover crop growth,” said lead researcher Meagan Schi-panski, who was a postdoctoral scholar at Penn State during the study.
Weed-suppression benefits occur during cash crop growth through long-term effects in which soil-carbon benefits accrue slowly over decades.
According to the National Resource Conservation Service, only five percent of cropped acres in the Chesapeake Bay area had cover crops planted annually in 2006 and 88 percent of agricultural fields had never been planted with cover crops.
In 2011, 52 percent of fields had cover crops planted at least once every four years and 18 percent had cover crops planted every year.
The NRCS said the increase has led to an average 78 percent reduction in soil loss, 35 percent less nitrogen surface loss, 40 percent less nitrogen subsurface loss, 30 percent reduction in phosphorus loss and a 50 percent reduction in soil carbon loss from the fields.
“When you visit a field in the fall or spring that is fallow and compare that to an adjacent field that is not, it becomes obvious why we see such an impressive impact of cover crops,” Kaye said.
“Bare soil is susceptible to erosion, there are no plants to hold the nutrients from being lost and there are no roots to fuel microbial activity and build organic soil matter. Cover crops solve these problems.”
The study did not compare stubble fields with cover crops.
Kaye said studies are continuing.
“One is to assess the value of having multiple cover crop species planted together,” he said.
“This is a popular strategy in the northern Great Plains, and the re-search there may be of great interest to Canadian farmers (because of the similar climates).”
