AMES, Iowa — Prairie strips can improve measures of soil health faster than expected, according to new research by Iowa State University scientists working in cooperation with the Soil Health Institute.
Prairie strips – 30-100 ft strips of herbaceous, perennial plants within crop fields – are designed to restore some of the benefits of Iowa’s native prairies while causing minimal impacts on crop production. Earlier studies have shown that prairie strips established in approximately 10% of a field can significantly increase biodiversity and pollinator habitat, reduce erosion and improve water quality. However, strips’ impacts on soil health have remained largely unexamined until now.
Findings from the new research, published recently in the Journal of Soil and Water Conservation, showed that prairie strips improved a number of soil health measures within 10-12 years. The perennial strips significantly improved eight out of 12 soil health indicators and increased several others at lower levels.
The greatest impacts were in:
- soil aggregate stability (up to 80%) – the ability of soil to resist erosion
- microbial biomass (up to 54%) – the mass of microscopic soil organisms driving nutrient cycling and carbon sequestration
- soil organic matter (up to 23%) – the living and dead carbon-containing part of the soil (central to healthy soils)
- maximum water-holding capacity (up to 7%) – the ability of soil to retain water
“It was an exciting surprise to see the degree of these changes over just a decade or so,” said Marshall McDaniel, associate professor of agronomy at Iowa State, who coordinated the study team. “It has been thought that it would take much longer to see some of these levels of change. Especially soil organic matter and maximum water-holding capacity”
Some measures continued to improve
Aggregate stability and maximum water-holding capacity increased throughout the study period. The increases in microbial biomass and soil organic matter plateaued over time, with the microbial biomass decreasing slightly at the end of the study period.
The study used a “paired chronoscope” approach to measure the changes. This “space-for-time” substitution used 15 paired control and treatment sites that were in prairie strips from 2- 13 years old and represented four of Iowa’s seven major landforms. Each pair had a prairie strip treatment and a cropland control managed in a conventional corn-soybean rotation. Most of the study sites were on private farmland. Six aspects of soil health were measured in the top six inches of the soil.
A more comprehensive assessment of soil health was conducted along the oldest (12-year-old) prairie strip at the Neal Smith National Wildlife Refuge near Prairie City. This research component was led by Elizabeth Rieke, a scientist with the Soil Health Institute, as part of its North American Project to Evaluate Soil Health Measurements.
Broader benefits
Cole Dutter, who completed his doctorate in sustainable agriculture and soil science while working on this project, was the lead author on the study and two related projects that looked at broader aspects of soil health under prairie strips. Additional findings from these studies showed:
- significant changes in microbial communities extending from the prairie strips far into adjacent cropland soils. The changes included elevated enzyme levels related to increased cycling of nutrients and carbon, with potential to boost nutrient availability to crops and enhance carbon storage.
- the effects of prairie strips on cropland soil moisture and plant-available nutrients extended more than 3 feet (up to 1 meter) outward from the strips, with minimal impacts on crop yields.
The research demonstrates the relatively quick benefits that can accrue from prairie strips. However, the strips represent only a fraction of a field.
“Some farmers we have worked with are interested in rotating their prairie strips after 10 years to spread the benefits across their fields,” said Lisa Schulte Moore, director of ISU’s Bioeconomy Institute and a collaborator on the study who developed the STRIPS conservation practice.
“Cole has initiated some interesting research looking at this idea," she said. "It is showing some long-term boosts to soil health and crop yields from rotating strips within fields. We look forward to having more results to share in the next year.”
As Dutter prepares to leave Iowa State for a faculty position at the California State University, Stanislaus, he plans to continue involvement in prairie strips research.
“Our related projects show that prairie strips are a relatively quick way to build soil health in the top of the soil profile. We think there is a lot of potential to expand these benefits throughout fields and even improve yields,” he said. “An area we need to learn more about is whether and to what degree that translates to storing carbon deeper in the soil profile.”
Soil health DIY tools
The researchers point out that the measurements of aggregate stability and water-holding capacity used in this study are based on easy, inexpensive techniques accessible to non-scientists. “These DIY tests are great tools that landowners can use to assess soil health on their own fields after implementing management changes like prairie strips,” McDaniel said.
- Aggregate stability, the measurement that showed the greatest improvement, can be done with a smartphone using a free Slakes app maintained by the Soil Health Institute. Using this app and a plastic petri dish, citizen scientists and farmers can measure a soil’s ability to resist erosive forces like wind and water.
- The maximum water-holding capacity method can also be done with little effort. Using just a funnel and coffee filter, anyone can measure this ability of their soil to hold water.
Sydney Pottebaum, then an undergraduate in agronomy, also contributed to the study. Funding came primarily from the Foundation for Food and Agriculture Research and the USDA Farm Service Agency, with additional support from the National Science Foundation and USDA Hatch funds.
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Contacts:
Marshall McDaniel, Department of Agronomy, 515-294-7947, marsh@iastate.edu
Ann Y. Robinson, Agriculture and Life Sciences Communications, 515-294-3066, ayr@iastate.edu