Minimizing the volume of agricultural chemicals utilized by farmers — such as fertilizers, pesticides, and herbicides — could diminish the amount of toxic runoff entering the environment while concurrently decreasing farmers’ expenses and possibly improving their yield. An ideal win-win-win situation.
A group of scientists at MIT, along with a spinoff enterprise they established, has created a method to achieve this goal. Their innovation applies a thin film around droplets as they are sprayed onto a field, significantly lowering their propensity to bounce off leaves and be lost on the ground. As a result, the treated droplets adhere to the leaves as intended.
The study is detailed today in the journal Soft Matter, in an article authored by recent MIT graduates Vishnu Jayaprakash PhD ’22 and Sreedath Panat PhD ’23, graduate student Simon Rufer, and MIT’s mechanical engineering professor Kripa Varanasi.
A recent investigation revealed that if farmers refrained from using pesticides, they could lose 78 percent of fruit, 54 percent of vegetable, and 32 percent of cereal production. Despite their significance, an absence of technology to monitor and optimize sprays has compelled farmers to depend on personal knowledge and heuristics to determine how to apply these chemicals. Consequently, these substances are frequently over-applied, resulting in runoff and chemicals contaminating waterways or accumulating in the soil.
Pesticides have a considerable impact on global health and the environment, the researchers emphasize. A recent study indicated that 31 percent of agricultural soils worldwide face high risks from pesticide contamination. Furthermore, agricultural chemicals represent a significant cost for farmers: In the U.S., they invest $16 billion annually solely on pesticides.
Enhancing the efficiency of spraying is one of the most effective methods to make food production more sustainable and cost-effective. Agricultural spraying fundamentally involves mixing chemicals with water and applying water droplets onto plant leaves, which are often naturally resistant to water. “Over more than a decade of research in my lab at MIT, we have built fundamental insights into spraying and the interaction between droplets and plants — examining when they bounce and the techniques we can utilize to enhance their adhesion and coverage,” Varanasi states.
The team had earlier discovered a technique to decrease the amount of liquid sprayed that rejects from the leaves it contacts, which involved employing two spray nozzles instead of one and spraying mixtures with opposing electrical charges. However, they noticed that farmers were hesitant to incur the costs and exert the effort required to update their spraying equipment to a two-nozzle configuration. Thus, the team sought a more straightforward solution.
They found that they could attain the same improvement in droplet retention using a single-nozzle setup that can be seamlessly adapted to current sprayers. Instead of imparting an electric charge to the pesticide droplets, they envelop each droplet with an extremely thin coating of an oily substance.
In their recent study, they conducted laboratory experiments using high-speed cameras. When they sprayed droplets without specialized treatment onto a water-repellent (hydrophobic) surface similar to that of many plant leaves, the droplets initially spread into a pancake-like shape, then reverted back into a sphere and bounced away. However, when the researchers coated the surface of the droplets with a minuscule amount of oil — constituting less than 1 percent of the droplet’s liquid — the droplets spread out and then remained fixed in place. This treatment increased the droplets’ “adhesion” by as much as a hundredfold.
“When these droplets make contact with the surface and begin to expand, they create this oily ring that effectively secures the droplet to the surface,” Rufer explains. The researchers explored a broad array of conditions, conducting hundreds of experiments, “with varying impact velocities, differing droplet sizes, varying angles of inclination, and all the factors that fully characterize this phenomenon.” While different oils displayed varying levels of effectiveness, all proved to be beneficial. “Regardless of the impact velocity and the types of oils used, we observed that the rebound height was considerably reduced,” he states.
The effect operates effectively with remarkably small quantities of oil. In their initial experiments, they utilized 1 percent oil compared to water, then examined a concentration of 0.1 percent, and even 0.01 percent. The enhancement in droplet adherence to the surface continued at a concentration of 0.1 percent but began to diminish at lower levels. “Essentially, this oily film functions as a mechanism to secure that droplet on the surface, as oil is very attracted to the surface and helps hold the water in position,” Rufer notes.
In their preliminary tests, the researchers used soybean oil for the coating, reasoning that it would be a familiar substance for the farmers involved, many of whom cultivated soybeans. However, it turned out that, although they were growing the beans, the oil was not part of their usual supply chain for agricultural use. In additional tests, the researchers discovered that several chemicals already frequently used by farmers in their spraying processes, known as surfactants and adjuvants, could be utilized instead, and some of these delivered identical benefits in maintaining the droplets on the leaves.
“This way,” Varanasi remarks, “we’re not introducing a novel chemical or changing existing chemistries in their fields, but utilizing materials they’ve already been familiar with for a long time.”
Varanasi and Jayaprakash established a company named AgZen to bring the system to market. To demonstrate the extent of their coating system’s effectiveness in retaining spray on plants, they first needed to create a framework to monitor spraying in real-time. This system, which they have named RealCoverage, has been implemented on farms ranging from a few dozen acres to hundreds of thousands, across various crop types, saving farmers between 30 to 50 percent on their pesticide costs simply by refining the management of existing sprays. The system is set to be utilized on 920,000 acres of crops in 2025, according to the company, including locations in California, Texas, the Midwest, France, and Italy. Incorporating the cloaking system with new nozzles, the researchers estimate, should lead to at least a twofold increase in efficiency.
“You could return a billion dollars to U.S. farmers if you merely saved 6 percent of their pesticide budget,” states Jayaprakash, the lead author of the study and CEO of AgZen. “In laboratory settings, we achieved 300 percent more product on the plant. This indicates we could realize substantial reductions in the quantity of pesticides that farmers are applying.”
Farmers had previously employed these surfactant and adjuvant substances to enhance spraying effectiveness, but they were combining them with a water solution. To produce any effect, they had to use significantly more of these resources, risking damage to the plants. The fresh coating system minimizes the quantity of these materials required while enhancing their efficacy.
In field trials conducted by AgZen, “we doubled the amount of product applied on kale and soybeans merely by altering the application of the adjuvant,” moving from being mixed in to functioning as a coating, Jayaprakash states. It’s convenient for farmers since “all they need to do is switch their nozzle. They’re optimizing the performance of all their existing chemicals while achieving more product on the plant.”
And it’s not limited to pesticides. “The truly exciting aspect is this method is applicable for any chemical applied to the leaf, whether it be an insecticide, herbicide, fungicide, or foliar nutrition,” Varanasi expresses. This year, they aim to launch the new spraying system on approximately 30,000 acres of farmland.
Varanasi asserts that given the anticipated growth of the global population, “the volume of food production needs to double, and we are constrained by many resources; for instance, we cannot double the amount of arable land. … This means every acre we currently cultivate must enhance its efficiency and yield more with fewer resources.” According to Varanasi, these improved spraying technologies, both for monitoring the process and coating the droplets, “I believe is fundamentally transforming agriculture.”
AgZen has recently secured $10 million in venture capital to facilitate the rapid commercial rollout of these technologies that can enhance the management of chemical inputs in agriculture. “The insights we are gaining from each leaf, in conjunction with our expertise in interfacial science and fluid dynamics, is providing us with unparalleled understanding of how chemicals are employed and formulated — and it’s evident that we can add value across the entire agrochemical supply chain,” Varanasi concludes. “Our mission is to leverage these technologies to deliver enhanced outcomes and decreased costs for the agricultural sector.”