Computer circuitry helps study soils

Bits and bytes boost agriculture

By Pat Melgares

This video shows other soil-related research projects at K-State, including the new digital agronomy collaboration research team.

Can an electronic circuit — not much larger than a postage stamp — help to speed up U.S. farmers’ goal to feed a hungry world?

It might, says Raj Khosla, if it’s taught to measure soil properties of a farm field so that in a matter of seconds, farmers can adjust water, nitrogen and other inputs to abundantly grow crops.

Think of it as farming in bits and bytes, in real time.

“The United States has constructed an agriculture innovation agenda that in the next 28 crop cycles — which gets us to the year 2050 — we want to grow 40% more food than what is currently grown,” said Khosla, a precision agriculture specialist, professor and head of the Kansas State University agronomy department in the College of Agriculture.

“But here is the caveat: We need to achieve this goal by using 50% less water and 50% less nitrogen applied to the crops, which are the two biggest drivers of crop production systems,” Khosla added. “This means we have to account for everything that goes into the water and nitrogen budget. We can’t leave room for error.”

For Khosla, it’s exciting work. For the past 10 years, he’s been methodically reducing the chance of error in several projects that focus on using sensors to measure soil moisture and nitrogen content.

If successful, farmers would be able to shun more expensive measuring equipment — sometimes a 10-to-12-foot tower in a field with probes snaking into the ground — costing hundreds to thousands of dollars, in favor of dozens to hundreds of biodegradable sensors scattered throughout a field.

Soil sensation

Soil moisture sensors estimate the volume of water in soil based on the principle of electrical resistance, or the soil’s ability to transmit electricity. As the water content of the soil increases, the resistance decreases and gives a predictable assessment of water content.

Other sensor-based measurements provide additional data specific to a field, such as the presence of plant-available nutrients to determine how much additional fertilizer should be applied or a crop’s reaction to such environmental conditions as temperature and light.

It’s research that Khosla has been investigating for a decade and has brought to K-State.

“Ten years ago, I was hypothesizing that someday we would have soil moisture sensors that we could literally throw out in a field, then ‘ping’ them with a computer to get a measure of that soil’s moisture content,” Khosla said.

Khosla began conducting field experiments in 2012 in collaboration with private partners that provided sensors mounted on a post and connected to cables that measured soil moisture at five depths. In that setup, Khosla determined that to cover a 22-acre field, a farmer would need about 100 sensor nodes — each at a cost of about $3,000.

“They were expensive,” he said. “Even today, they are cost prohibitive for a farmer. Installing those sensors is labor intensive and it’s a logistical nightmare to have 12-foot-tall posts sticking out of your 22-acre field at such a high density.”

Those early experiments, though, served a purpose: to fuel the research group’s motivation to provide a low-cost option that could still gather detailed information of the farmer’s entire field.

Getting rid of guesswork

Now, Khosla is co-leading a collaborative team that is building on those early experiments. In 2018, Khosla and his colleagues at the University of Colorado Boulder and the University of California, Berkeley received a U.S. Department of Energy grant that funds high-risk/high-reward projects through the Advanced Research Project Agency.

The team of researchers includes materials scientists and computer and electrical engineers from the collaborative institutions. Other K-State agronomy researchers involved include Jeff Siegfried and Dipankar Mandal, both postdoctoral research fellows; Wub Yilma, doctoral student; and Ross Unruh, assistant scientist.

Together, the researchers have keyed in on moving agriculture further into the digital age.

The biodegradable sensors that they are working to test, evaluate and assist with design and redevelopment will provide the capability of measuring at high spatial densities. That would allow researchers to estimate soil moisture at every inch of a field and provide huge volumes of data that are crunched by computer algorithms to build an easily readable guide for the farmer.

“There is no spot in the field where there will be guesswork,” Khosla said.

Farmers already can apply water, nitrogen and other nutrients in very precise ways, using such current technologies as variable rate irrigation that can be adjusted to provide different rates of water in a field, Khosla said. But knowing the field’s needs, foot by foot, is limited to measurements provided by satellite images or unmanned aerial vehicles. Those are good ways to accommodate a field’s needs, but still not entirely precise, diagnostic or immediate.

“One idea is that as a pivot is applying water in a field, you can ping sensors that are lined up in the next 20, 50 or even 100 feet of the pivot arm,” Khosla said. “That information is sent back to the computer to re-create the real-time soil-moisture data surface that the pivot is encountering while it is applying the water, and the farmer or artificial intelligence-based decision tools can change the rate of application if necessary. I think that’s going to be a big deal.”

If farmers were to deploy 100 sensors throughout a field, the sensor cost — at 50 cents to $1 each — would be $50 to $100. Setting them up would be as simple as walking the field and tossing and inserting them about. Because they would be biodegradable, they would never have to be collected.

The eco-friendly biodegradable chips, which Khosla thinks will start to deteriorate in about 200 days, are not yet available. Currently, the research team is using larger, more expensive circuits that are not biodegradable to make sure the huge volumes of data they are collecting can be processed by computers using algorithms developed by K-State researchers to translate data that enables farmers to make better decisions.

“We can only manage what we can measure,” Khosla said. “If we can’t precisely measure the resources that we’re trying to manage, then we won’t be able to help farmers. I think that’s particularly true for these two major inputs in crop production systems — water and nitrogen — that are environmentally so sensitive and important.”

But this work is the first step toward an exciting new agricultural era that involves more sensors and data-driven decisions.

“These types of technologies often are for organizations with a very high demand for information technology. They’re usually the first ones to get their hands on it,” Khosla said. “Well, this time it happens to be agriculture. It’s very exciting to be in that environment.”

A lab on a chip

K-State chemical engineer Ryan Hansen also is capitalizing on the power of miniaturized sensors as he and his team build what he terms a “lab on a chip” that studies the interactions among many types of microorganisms.

Among other potential uses, the technology may aid in improving bioinoculants on farm crops, probiotics for human health and antibiotics for medicine.

The technology is called the Microwell Recovery Array, or MRA. The device uses small wells to screen tens of thousands of interactions among microbes in one experiment. In its current form, Hansen said, it is designed to find bacteria that have the strongest interactions with a specific microorganism, which may be a pathogen but could also be beneficial bacteria.

“Microorganisms are social organisms and they interact with each other in symbiotic, competitive or antagonistic ways in their natural ecosystems,” said Hansen, associate professor, Steve Hsu Keystone research scholar and Warren and Gisela Kennedy Keystone research scholar in the Carl R. Ice College of Engineering. “It is important to fundamentally understand these interactions to help us predict how diverse collections of microbes function together.”

He notes that many ecosystems — such as soil and plant roots — harbor diverse microbial communities.

“Finding interactions that influence the most important microbes can be a very daunting task, especially with the limited experimental techniques available in the standard microbiology laboratory,” said Hansen, who is in the Tim Taylor Department of Chemical Engineering.

MRA now makes overcoming the challenge achievable.

“In the case of a probiotic, we want to find symbiotic bacteria that support its function,” Hansen said. “In the case of a pathogen, we want to find antagonistic bacteria that can defend against it. With our screening technology, we have shown that we can quickly find both types of interacting cells in just one experiment, equivalent to what would likely take months to do using standard methods.”

Hansen said understanding interactions among microbes may also help in developing bio-based fertilizers for farm crops — and decrease the need for chemical fertilizers. Bio-based fertilizers are limited currently because they are often unreliable, he noted.

“Developing more reliable biofertilizers is very important for establishing sustainable agricultural practices,” Hansen said.

K-State researchers are using MRA technology to screen for symbiotic interactions between a nitrogen-fixing bacterium called Azospirillum brasilense and bacteria native to corn root. Hansen said it is likely that symbiotic bacteria can be combined with A. brasilense to improve its efficiency and reliability as a biofertilizer.

“In small-scale laboratory studies, we have seen that co-inoculating A. brasilense with symbiotic mixtures of bacteria accelerates early stage corn growth compared to inoculating with A. brasilenseonly,” Hansen said.

In addition to developing effective bio-fertilizers, Hansen said the ongoing K-State work includes using the MRA to screen soil and plant root samples to discover bacteria that are useful as biocontrol agents, which could reduce the incidence or severity of diseases caused by plant pathogens. The MRA also is helping to discover soil bacteria that can be used to help retain moisture during drought.

Hansen’s research has been funded by the National Science Foundation and has been published in journals such as ACS Applied Bio Materials, Biomacromolecules and Frontiers in Microbiology.

Hansen as well as Thomas Platt, assistant professor of biology in the College of Arts and Sciences, and other researchers also were awarded a related patent, “Hydrogel Membrane and Methods for Selective Retrieval of Microbial Targets.”

Sidebar
Keeping lead in its place

In a vacant lot east of downtown Kansas City, Missouri, Ganga Hettiarachchi, Kansas State University professor of soil and environmental chemistry, leads her research team in lining out a grid. The researchers hope the work will give them important clues on how to reduce the risk of human exposure to lead.

“We are dividing the sections in this area so we can map the concentration of lead on the entire site,” said Ruwandi Kumarasinghe, a member of the team and a research associate in the agronomy department in the College of Agriculture.

The Missouri Department of Health and Senior Services reports that lead-based paint and contaminated dust are the most common sources of exposure in the U.S. Soil often becomes contaminated from natural weathering of exterior-based paint from houses and other structures. Areas around houses built before 1978 — when lead-based paint was banned — are more susceptible to lead contamination.

In early 2022, Hettiarachchi received $700,000 from the U.S. Department of Housing and Urban Development, or HUD, to study the presence of lead in vacant city lots and as many as a dozen brownfield sites, or land previously developed that is no longer in use and has known or suspected contamination.

In 2021, the Centers for Disease Control and Prevention estimated more than 500,000 U.S. children under age 6 have blood lead levels higher than 5 micrograms per deciliter, which at that time was the level at which recommended public health actions be initiated. The reference value is now at 3.5 micrograms per deciliter. Lead exposure can stunt childhood brain development, as well as cause damage to the brain and nervous system in children and adults, among other health risks.

Hettiarachchi said basic soil chemistry could be key to immobilizing or reducing direct exposure to lead and other contaminants in soil. For example, adding phosphorus sources to soil to convert lead into a less soluble form can be combined with common management practices, such as applying mulch or wood bark in home landscapes.

At the test plots in Kansas City, Hettiarachchi and her research team are applying soil amendments to try and find the best ways to decrease the bioavailability of lead to children and adults.

“People think soil chemistry is basic science, and most of the time it is,” she said. “But in this case, it is basic science that can be applied to public health.”

Amy Roberts, the project manager for the Kansas City, Missouri Health Department’s Childhood Lead Poisoning Prevention and Healthy Homes program, notes that Kansas City has some zip codes where the lead poisoning rate is nine times the national average — alarming numbers that she says need to be addressed.

“To our knowledge, there are no studies evaluating the benefits of adding in situ stabilization methods to current state and local lead poisoning mitigation programs,” Hettiarachchi said.

It’s likely that many urban areas across the U.S. have similar risks, and K-State’s work is drawing an attentive eye across the country.

“If we are successful in Kansas City, and because the Environmental Protection Agency manages the brownfield program, and HUD is assisting cities and states in addressing lead poisoning issues, the lessons learned can be adopted by any other city around the nation,” Hettiarachchi said. “Kansas City could be a model city.”

K-State’s work is in partnership with the city of Kansas City, Missouri; the EPA; and Children’s Mercy Hospital.