With winter weather blanketing northern areas, researchers are finding that seeding cover crops can lead to much warmer field temperatures.
A study by researchers at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., found the darker leaf and stem surfaces of cover crop plants absorb more heat from the sun than a snow-covered field, especially with cover crops that are 12 inches taller than the snow depth. In fact, the scientists found that tall, leafy cover crops can dramatically influence the surrounding ground surface temperature even when partially covered by 12 inches of snow.
With concerns growing about climate change, these researchers are urging no-tillers to consider several factors when it comes to effectively managing their cover cropped acres, including factors that are unfortunately somewhat at odds with each other. These include:
Seeding cover crops could lead to warmer temperatures that enable no-tillers to plant cash crops earlier in the spring.
Cover crops can help reverse the effects of climate change by capturing and storing carbon in the soil.
The added warmth captured by over-wintering cover crops may contribute to global warming.
Tall Vs. Short Plants
The NCAR researchers used computer simulations to look at the impact of cover crop height and plant leafiness based on the amount of snow cover and field temperatures. They looked at cover crops that were 4-, 12- and 20-inches tall along with plants having either one or four leaves.
Leaves Capture Heat
The researchers found leafy cover crops can dramatically warm the ground surface under snow cover in the northern United States and southern Canada when these plants protrude above the height of the snow pack. While a field with bright snow cover will reflect sunlight back into space, they say heat that is absorbed by the cover crop stems and leaves will instead warm the ground by as much as a half dozen degrees.
The leafy cover crops that were tall enough to protrude above the snow absorbed more of the sun’s energy than did the reflective snow in non-cover-cropped fields, says Danica Lombardozzi, a NCAR plant ecologist. Tall cover crops that were less leafy also increased temperatures, although the increase was smaller and the warming was much less widespread.
After doing the computer analysis, the, NCAR scientists concluded that while all three of the plant scenarios warmed the atmosphere, the tall and leafy plants produced the most significant effect in heating up the surrounding ground area. The studies were based on a snow depth of 12 inches.
When 4-, 12- and 20-inch tall cover crop heights were compared, there was a big difference with increased warming when the snow was 12 inches deep, adds Lombardozzi. While leafiness was a big factor, crop height determined whether or not the plants were actually sticking up above the variable snow pack. But even though cover crop plant height tends to matter more than leafiness, the impact of the two together can be strong.
“This work illustrates that cover crops, if they stick above the snow pack in the winter, can significantly increase winter temperatures,” she says. “However, the winter warming can be mitigated by selecting and planting short cover crops and/or mowing or grazing the cover crops before snowfall.”
She adds that by selecting shorter cover crops, growers will be able to reduce the impact of winter warming while still getting all the benefits of planting cover crops.
Global Warming Worries
Although seeding cover crops is a valuable tool to maintain yields and minimize nitrogen losses as the climate seems to continue to get warmer, these scientists say the selection of cover crop varieties by growers may be the most important factor critical in combatting climate change concerns.
While cover crops are really good for fertility, productivity and even carbon storage, unfortunately there’s the possibility that these soil-protecting covers could have a detrimental effect on climate change. Yet the data highlights the need for further evaluation of the role of cover crops in helping reduce climate change concerns rather than encouraging more global warming.