Cover crops comparable to no-till
Climate-change mitigation and adaptation may be additional, important ecosystem services provided by cover crops, said Jason Kaye, professor of soil biogeochemistry in the College of Agricultural Sciences at Penn State. He suggested that the climate-change mitigation potential of cover crops is significant, comparable to other practices, such as no-till.
"Many people have been promoting no-till as a climate-mitigation tool, so finding that cover crops are comparable to no-till means there is another valuable tool in the toolbox for agricultural climate mitigation," he said.
In a recent issue of Agronomy for Sustainable Development, Kaye contends that cover cropping can be an adaptive management tool to maintain yields and minimize nitrogen losses as the climate warms.
Collaborating with Miguel Quemada in the Department of Agriculture Production at the Technical University of Madrid in Spain, Kaye reviewed cover-cropping initiatives in Pennsylvania and central Spain. He said that lessons learned from cover cropping in those contrasting regions show that the strategy has merit in a warming world.
The researchers concluded that cover-crop effects on greenhouse-gas fluxes typically mitigate warming by 100-150 grams of carbon per square meter per year, which is comparable to, and perhaps higher than, mitigation from transitioning to no-till. The key ways that cover crops mitigate climate change from greenhouse-gas fluxes are by increasing soil carbon sequestration and reducing fertilizer use after legume cover crops.
"Perhaps most significant, the surface albedo change (the proportion of energy from sunlight reflecting off of farm fields due to cover cropping) calculated for the first time in our review using case-study sites in central Spain and Pennsylvania, may mitigate 12 to 46 grams of carbon per square meter per year over a 100-year time horizon," Kaye wrote.
"Cover crop management also can enable climate-change adaptation at these case-study sites, especially through reduced vulnerability to erosion from extreme rain events, increased soil-water management options during droughts or periods of soil saturation, and retention of nitrogen mineralized due to warming," he said.
Not a primary management practice
Despite the benefits, Kaye is not necessarily advocating that cover crops be planted primarily for the purposes of climate-change mitigation or adaptation. Instead, he thinks the most important conclusion from his analysis is that there appear to be few compromises between traditional benefits of cover cropping and the benefits for climate change.
"Farmers and policymakers can expect cover cropping simultaneously to benefit soil quality, water quality and climate-change adaptation and mitigation," he wrote.
"Overall, we found very few tradeoffs between cover cropping and climate-change mitigation and adaptation, suggesting that ecosystem services that are traditionally expected from cover cropping can be promoted synergistically with services related to climate change."
About a year ago, a group of researchers discovered Palmer is resistant to the herbicide class known as PPO-inhibitors, due to a mutation —known as the glycine 210 deletion — on the PPX2 gene.
“We were using a quick test that we originally developed for waterhemp to determine PPO-resistance based on that mutation. A lot of times, the test worked. But people were bringing in samples that they were fairly confident were resistant, and the mutation wasn’t showing up. We started to suspect there was another mechanism out there,” says University of Illinois molecular weed scientist Patrick Tranel.
Tranel and his colleagues decided to sequence the PPX2 gene in plants from Tennessee and Arkansas to see if they could find additional mutations. Sure enough, they found not one, but two, located on the R98 region of the gene.
“Almost all of the PPO-resistant plants we tested had either the glycine 210 deletion or one of the two new R98 mutations. None of the mutations were found in the sensitive plants we tested,” Tranel says.
Furthermore, some of the resistant plants had both the glycine 210 deletion and one of the new R98 mutations. Tranel says it is too early to say what that could mean for those plants. In fact, there is a lot left to learn about this resistance mechanism.
“We don’t know what level of resistance the new mutations confer relative to glycine 210,” Tranel says. “There are a lot of different PPO-inhibiting herbicides. Glycine 210 causes resistance to all of them, but we don’t know yet if the R98 mutations do.”
The team is now growing plants to use in follow-up experiments. Tranel hopes they will be able to determine how common the three mutations are in any given population. “That way,” he says, “when a farmer sends us a resistant plant and it doesn’t come back with the glycine 210 deletion, we will be able to tell him how likely it is that he’s dealing with another one of these mutations.”
In the meantime, other research groups or plant testing facilities could use the new genetic assay to detect the mutations in Palmer samples. Tranel hopes they will. “The more labs testing for this, the more we learn about how widespread the mutation is,” he says.
The article, “Two new PPX2 mutations associated with resistance to PPO-inhibiting herbicides in Amaranthus palmeri,” is published in Pest Management Science. The work was supported by a grant from the USDA’s National Institute of Food and Agriculture.
Annually, diseases, weeds, and insects are estimated to cause more than $1.3 billion in losses for sunflower growers. To combat this, researchers are preserving the genetic diversity of wild sunflowers. Wild plants retain the genes needed to resist pests and survive in different environments.
A group of researchers at the University of Illinois wanted to know which farmers are most likely to adopt multifunctional perennial cropping (MPC) systems – trees, shrubs, or grasses that simultaneously benefit the environment and generate high-value products that can be harvested for a profit.
"We surveyed farmers in the Upper Sangamon River Watershed in Illinois to learn their attitudes about growing MPCs on marginal land. We then looked at their demographic data to classify people into different categories related to their adoption potential," says University of Illinois agroecologist Sarah Taylor Lovell.
Using statistical clustering techniques, the team discovered that survey respondents fell into six categories. The "educated networkers" and "young innovators" were most likely to adopt MPCs. On the other end of the spectrum, survey respondents classified as "money motivated" and "hands-off" were least likely to adopt the new cropping systems.
The goal of categorizing farmers was to tailor strategies for each group, given their general attitudes. "If they're very unlikely to adopt at all, we probably wouldn't spend a lot of time worrying about those groups," Lovell explains.
However, Lovell thinks some low-likelihood adopters could be swayed. "One of the groups--the one we called "money motivated" – was really connected with GPS in their yield monitoring, so we thought we could target that. We could review high-resolution maps of their farms to point out the areas that are unproductive for corn and soybeans. We'd try to make the case that alternative perennial systems could bring in profits," Lovell says.
High-likelihood adopters were motivated by environmental concerns, and were especially interested in converting marginal land to bioenergy crop, hay, or nut production systems. "Farmers were probably most familiar with bioenergy grasses and hay," Lovell explains. But it was important to them that an existing market was in place for MPCs products.
Another major factor was land tenancy. Considering that most MPC crops don't mature for years after planting, rental contracts would need to account for the long-term investment.
"The person leasing the land might be really interested in agroforestry or perennial cropping systems," Lovell says. "The lease arrangement has to be long enough that the farmer will get back their investment in that period. For example, some of the nut crops take a long time to mature. But if you integrate some of the fruit shrubs, they'll become productive in maybe 3-4 years. You could get an earlier return on investment in those cases."
Lovell's graduate students – housed in the crop sciences department at U of I – are now following up with several of the farmers who were interested in MPCs and offering custom designs to establish the new cropping systems on their land.
"That was part of the overall goal for this study. We wondered if the barrier to adoption is a lack of information about design options and the economic potential," Lovell says. "If we overcome that barrier by developing good planting plans, projecting the market economics, and providing them with that information, will that help them implement the change?"
Researchers tested the effects of increased CO2 and warmer temperatures on plant water use. Although increased carbon dioxide and warmer temperatures generally improve photosynthesis, in these experiments the researchers found that pores on plant leaves, known as the stomata, were predicted to narrow in these conditions, reducing the amount of moisture plants release into the air.
Although this change may mean some plants are more efficient in their water use in some arid regions, overall this change in plant physiology will have its own climate effects, resulting in less rainfall in some regions, damaging plants and crop yields, says Qianlai Zhuang, professor of earth and atmospheric science at Purdue University.
“This study reveals that while increasing atmospheric carbon dioxide can directly strengthen plant uptake of CO2, it can also reduce plant transpiration, influence global precipitation patterns, and increase warming locally,” he says.
In many terrestrial ecosystems, precipitation is from water recycled to the atmosphere by plants upwind, affecting both precipitation and temperatures, says coauthor Lisa Welp, assistant professor of biogeochemistry in the department of earth, atmospheric, and planetary Sciences.
“The role that terrestrial vegetation plays in rainfall recycling on land is often simplified or overlooked, but it’s a key player in determining regional precipitation patterns and, therefore, productivity in water-limited ecosystems,” Welp says.
“If some plants reduce their transfer of water to the atmosphere by reducing transpiration rates, this results in regional declines in precipitation. It also results in local heating because evaporating water from plant leaves acts like an air conditioner, keeping surface temperatures cooler.”
Overall, the effect is strong enough that there is no net increase in global agricultural production, Zhuang says. In fact, as carbon dioxide increases globally, the modeling showed that plant life in most regions of the world suffers considerably due to rising temperatures and decreased precipitation.
“You cannot look at just one effect in isolation, such as photosynthesis, and make a determination of how it will affect global crop production,” Zhuang says. “There are both direct and indirect effects, and both should be considered.”
Atmospheric carbon dioxide has increased from 280 parts per million before the Industrial Age, which began in the late 1700s, to the current level above 400 parts per million.
Zhuang and graduate student Peng Zhu devised six model experiments using historic climate data from 1850 to 2011. They found that although a few areas would see improved plant growth – including parts of Canada, most of Madagascar, and the southern tip of India – other regions on the planet would suffer.
“This study indicates that the net CO2 fertilization effect will be overestimated unless vegetation-climate feedback effects are taken into account,” Zhu says.
Only three plant species -- rice, wheat, and maize -- account for most of the plant matter that humans consume, partly because of the mutations that made these crops the easiest to harvest. But with CRISPR technology, we don't have to wait for nature to help us domesticate plants, argue researchers.
Some scientists say the solution could lie in crops' DNA and are making “gene catalogs” to help farmers grow healthier produce that can withstand climate change. | READ MORE
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