Prairie strips can improve soil health

AMES — 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-foot 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 nearly 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 strips increased soil aggregate stability (the ability of soil to resist erosion) by 80%; microbial biomass (the mass of microscopic soil organisms driving nutrient cycling and carbon sequestration) by 54%; the soil organic matter (the living and dead carbon-containing part of the soil central to healthy soils) by 23%; and the maximum water-holding capacity (the ability of soil to retain water) by 7%.

“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.”

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 between two and 13 years old and represented four of Iowa’s seven major land forms.

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 Riecke, a scientist with the Soil Health Institute, as part of its North American Project to Evaluate Soil Health Measurements.

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 three feet 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.

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.