AMES, Iowa - Imagine buying a dozen eggs at a grocery store, but when you get home and open the carton, there's only a half dozen inside because you weren't buying a dozen eggs. You were buying approximately 12 eggs, plus or minus six.
That's how Andrew Vanloocke often describes a project he has led to develop a more reliable way to estimate how tillage, the methods farmers use to prepare their farmland for planting crops, affects soil carbon levels and yield. The accuracy of those estimates is important to farmers, as yield is always a baseline concern and sufficient levels of organic carbon make soil more productive and stable.
Tillage's impact on soil carbon is also important to companies that pay farmers to reduce tilling to help meet corporate carbon emissions goals.
"These companies want the best, most transparent estimates possible to ensure they're getting a dozen eggs instead of six," said Vanloocke, an associate professor of agronomy at Iowa State University.
A database built by Iowa State researchers aims to provide more certainty by digging deep into the effects of tillage, integrating the results of more than 250 peer-reviewed studies.
"We've taken a lot of useful science already done by many different people in many different places and put it together in a way that can be even more useful," Vanloocke said.
Going granular
The project began about five years ago when Zach Simpson - at the time a post-doctoral research associate for Marshall McDaniel, an associate professor of agronomy at Iowa State - began collecting data to analyze how tillage affects multiple aspects of cropping systems.
"I think he was just tired of everyone coming up with different answers," Vanloocke said of Simpson, now a researcher at Aarhus University in Denmark.
Studies included in the database were identified by reviewing two meta-analysis papers that collected global research into how tillage affects soil organic carbon and crop yield. Including yield in the analysis was important because while no-till farming typically increases soil carbon, it also tends to reduce yield, McDaniel said. The balance between no-till's benefits and tradeoffs needs to be better understood, he said.
"One of the goals in science, especially in environmental science, is to inform decision-making. So, we have to understand the consequences for yield," he said.
Limiting their analysis to research based in North America, the Iowa State team extracted detailed information often missed in the average effects estimated by meta-analysis studies - soil conditions, climate and the presence of irrigation, for instance. Tillage was classified on a continuum of intensity instead of an either-or basis, five stages ranging from deep soil-turning to completely hands-off no-till.
"You don't get granular data unless you comb through the papers and find all those modifying factors," said McDaniel, who added that facilitating future analysis is one of the reasons scientists should publish research data and thoroughly describe their methods.
Private support, public data
The ISU database didn't reveal unexpected trends, based on the researchers' initial analysis. In many agricultural settings, lower-intensity tillage improves soil organic carbon and causes some yield loss. Higher-intensity tillage generally does the opposite. The effects of low- and no-till appear to be more pronounced when they follow higher-intensity methods.
But having a rich database on tillage and soil carbon has been valuable for the sustainability team at Eocene Environmental Group, a West Des Moines-based environmental consulting firm that helped fund the research.
One of Eocene's services is helping businesses navigate carbon markets to reduce their emissions footprint under frameworks such as the Science Based Targets initiative, which often involves paying farmers to use practices that will store more carbon in soil. The firm contacted Iowa State about four years ago, wondering if any researchers would be interested in taking on a project much like what Simpson had already started.
Uncertainty is one of the biggest challenges in carbon markets due to the relative lack of field-tested soil organic carbon research, said Gabe McNunn, Eocene vice president of environmental modeling and data science.
"There just aren't enough studies focused clearly on practices - here's the baseline and here's the difference the practice made compared to the control," he said. "That sort of research is very limited."
Also, predicting how much carbon soil will hold in different cropping systems depends on many complex factors, including how slowly soil carbon levels change and how difficult it is to accurately measure, McDaniel said.
Those challenges compelled Eocene to partner with Iowa State to wring as much insight as possible from the existing body of research, said McNunn, who earned his bachelor's and master's degrees in mechanical engineering and a doctorate in environmental science at Iowa State. It's also part of the reason Eocene wanted the data to remain public.
"We want other people to see and use the data so that, hopefully, when they take new measurements or new studies are available, they can be added. We envision this as an ongoing and collaborative effort that improves over time," he said.
What's next
Eocene is continuing to partner with Iowa State researchers, who are starting to work on a similar project analyzing research into the impact of planting cover crops. No-till and cover crops are the top farming methods carbon markets support, McNunn said.
McDaniel said he envisions these kinds of databases becoming more user-friendly, powering tools that are accessible for farmers. Artificial intelligence will help speed up the process of synthesizing existing research to inform and enrich management decisions.
"That's definitely where agriculture's future is heading," he said.
The projects also show why Iowa State last fall launched a new undergraduate program in digital and precision agriculture, Vanloocke said. A strong foundation in both agriculture and data analysis is a skill set in need.
"This is exactly the sort of work our digital and precision agriculture graduates will be prepared to work on," he said.
