Mixed Crops Provide Benefits for Agricultural Landscapes

There are often too few flowering plants in agricultural landscapes — one reason for the decline of pollinating insects. Researchers at the University of Göttingen recently investigated how a mixture of fava beans and wheat affects the number of pollinating insects. They found that mixed fields of fava beans and wheat, compared with monocultures of fava beans, are visited equally often by foraging bees. Their results were published in the journal Agriculture, Ecosystems & Environment.

The researchers observed and counted foraging honeybees and wild bees in mixtures of wheat and fava bean and in pure cultures that only contained fava beans. “We had expected that the mixed crops, with fewer flowers, would be visited less frequently by bees for foraging than single crops,” said PhD student Felix Kirsch. “To our surprise, this was not the case.”

This could be due to several reasons. “Our mixed cultures were less dense than pure cultures, which possibly increased the visibility of the flowers. This might have attracted the similarly large number of bees to the mixed cultures,” suggested Dr. Annika Hass. “In addition, reduced competition between the fava bean plants in mixed cultures could mean that they can invest more resources in the production of nectar and pollen to increase their attractiveness to bees,” added Professor Wolfgang Link.

Mixed cultivation of wheat and fava beans may have other advantages for crop production. For instance, yields per bean plant were higher in mixed crops than in pure cultures. “Cereal crops can be ecologically enhanced by adding legumes such as beans or lentils. This can make a valuable contribution to increasing the abundance of flowers on the arable land and thus counteracting pollinator decline,” concluded Hass.

Carbon Intensity of Biofuels Is No Better than Gasoline 

Biofuels are a part of many proposed strategies to reduce anthropogenic greenhouse gas emissions and to limit the magnitude of global warming. The U.S. Renewable Fuel Standard is the world’s largest existing biofuel program, guiding nearly half of global biofuel production. Yet despite its prominence, there has been limited empirical assessment of the program’s environmental outcomes. 

A new study in the Proceedings of the National Academy of Sciences has found that the production of corn-based ethanol in the United States has failed to meet the policy’s own greenhouse gas emissions targets and has negatively affected water quality, the area of land used for conservation and other ecosystem processes. This is without even considering the likely international land-use effects of the policy.

The team’s findings suggest that profound advances in technology and policy are still needed to achieve the intended environmental benefits of biofuel production and use.

Combining econometric analyses, land-use observations and biophysical models, the researchers estimated the realized effects of the RFS, both in aggregate and down to the scale of individual agricultural fields across the United States. They found that the RFS increased corn prices by 30 percent and the prices of other crops by 20 percent; this in turn expanded U.S. corn cultivation by 2.8 Mha (8.7 percent) and total cropland by 2.1 Mha (2.4 percent) in the years following policy enactment (2008 to 2016). These changes increased annual nationwide fertilizer use by 3 to 8 percent and increased water-quality degradants by 3 to 5 percent. 

The team also found that the carbon intensity of corn ethanol produced under the RFS is no less than gasoline and is likely at least 24 percent higher. According to the researchers, “While improvements in production efficiency have likely reduced the carbon intensity of corn ethanol since inception of the RFS, the previously underestimated emissions from US land conversion attributable to the policy are enough to fully negate or even reverse any GHG advantages of the fuel relative to gasoline.”

These tradeoffs must be weighed alongside the benefits of biofuels as decision-makers consider the future of renewable energy policies and the potential for fuels like corn ethanol to meet climate mitigation goals.

Integrating Ground, Airborne and Satellite Imagery to Map Tilled Land

According to national USDA statistics, no-till and conservation tillage are on the rise, with more than three quarters of corn and soybean farmers opting for the practices to reduce soil erosion, maintain soil structure and save on fuel. However, these estimates are based primarily on farmer self-reporting and are only compiled once every five years, potentially limiting accuracy.

In a new study, University of Illinois scientists demonstrated a way to accurately map tilled land in real time by integrating ground, airborne and satellite imagery.

“We’ve shown remote sensing can quantify regional-scale tillage information in a cost-effective manner. This field-level information can be used to support growers in their management practices, as well as to support agroecosystem modeling and provide tools to the USDA to verify their census data,” said the study’s lead author, Sheng Wang.

Wang and the research team took photos of the ground at participating field sites throughout Central Illinois, generating 6,719 GPS-tagged images. They then arranged for an airplane equipped with high-powered hyperspectral sensors to fly over the region. The airborne system scanned 40,000 acres per hour and captured rich spectral signatures of the ground at a scale of about half a meter.

Wang fed the ground photos into a computer that learned to differentiate bare ground from crop residue, a hallmark feature of no-till and conservation tillage. After training on labeled ground images, the computer could interpret and predict hyperspectral images from the airborne sensor with about 82 percent accuracy. Using this ground-to-air upscaling as a model, the computers then developed an algorithm to scale up again — this time from the air to space, using satellite data.

Compared to upscaling directly from the ground to the satellite, which was only accurate about 22 percent of the time, according to a separate analysis in the study, the airborne layer increased mapping accuracy to 67 percent.

Although the method was tested in Champaign and surrounding Illinois counties, the team is working to scale the technology to the broader Midwest and the nation. Now that airborne sensors and computers have been trained to detect evidence of tillage using ground images, it should be possible to forego or minimize ground photos in the next iteration.

Circadian Clock Controls Sunflower Blooms, Optimizing for Pollinators

An internal circadian clock controls the distinctive concentric rings of flowering in sunflowers, maximizing visits from pollinators, according to a new study in eLife from plant biologists at the University of California, Davis.

A sunflower head is made up of hundreds of tiny florets. Because of the way sunflowers grow, the youngest florets are in the center of the flower face and the most mature at the edges, forming a distinctive spiral pattern from the center to the edge.

An individual floret blooms over a couple of days: on the first day, it opens the male part of the flower and presents pollen; on the second day, the female stigma unfold to receive pollen. Somehow, florets coordinate so that they open in concentric rings, starting from the edge and moving inwards on successive days, with a ring of female flowers always outside the earlier-stage, pollen-bearing male flowers.

Pollinating bees tend to land on the ray petals around a sunflower head and walk toward the center, said senior author Stacey Harmer, professor of plant biology, UC Davis College of Biological Sciences. That means that they will pick up pollen after they have walked over the female florets and then carry it to a different flower head.

Harmer and postdoctoral researcher Carine Marshall wanted to understand how the spiral pattern of florets turns into concentric rings of flowering. Harmer’s lab had previously established that circadian rhythms control how growing sunflowers track the sun during the day.

The internal circadian clock of a plant or animal runs on a cycle of about 24 hours, allowing different genes to be activated at different times of day. Natural day/night cycles keep this internal clock synchronized to actual day time. Changing the length or day light, or darkness, can reset the clock. In sunflowers, continuous light disrupts the clock entirely.

The researchers took time-lapse videos of sunflowers grown in different light/dark or temperature conditions. They found that the plant’s circadian clock controls the opening of florets. When the clock was disrupted by growing plants in continuous light, florets did not open in concentric rings, but only by age, starting at the edge and moving to the center in a continuous gradient.

When plants that had been grown with a disrupted clock were moved outside, they attracted fewer pollinators than normal sunflowers. “We think that being able to coordinate in this way makes them a better target for bees,” Harmer said. “It’s a strategy to attract as many insects as possible.”

As farmers adapt to a changing climate, it will become increasingly important to make pollination as efficient as possible in crops that require it, Harmer said. Understanding how the circadian clock and the environment affect flowering will help breeders develop cultivars that flower at the optimal times of day to promote pollination, despite climate change and declining insect populations, she said.

Licorice Leaf Extract a Promising Plant Protectant

Pesticides have proven effective in protecting crop yield against plant pathogens, but the environmental detriment to nontarget organisms has prompted a tug-of-war between organic and conventional agriculture practices. This poses the question: How can growers and farmers sustain their business in the safest, most responsible way? While copper, a naturally occurring pesticide, has been widely implemented in response to this question, growers need additional biocontrol methods to reduce copper use and further contribute to sustainable solutions.

A study recently published in Plant Disease reveals another promising biocontrol alternative. Since the licorice plant has broadly benefitted other industries, the researchers tested its impact as a pesticide and discovered that the licorice leaf extract is a potent bactericide and fungicide. Corresponding author Adam Schikora explains, “In the pharmaceutical, cosmetic, and food industries, the interest focuses primarily on roots of the licorice plant. The leaves and upper parts of the plant are byproducts and often neglected. However, we show their potential as a base for plant-protection products, which may be utilized in both conventional and organic agriculture systems.”

Using plant efficacy trials, the researchers tested the impact of licorice leaf extract on the virulence of common, highly pathogenic bacteria in the model plant Arabidopsis and in tomato. Their results demonstrated that licorice leaf extract modulates plant immune responses to pathogens, involving both salicylic acid and ethylene-based responses. The extract also acts against a particular late blight-causing oomycete that is resistant to metalaxyl, the active ingredient in several synthetic fungicides.

These exciting results offer a potential way to naturally control plant diseases caused by a vast range of pathogens, including bacteria and oomycetes.