Improving Outcome Predictability, Multifunctionality and Cost-effectiveness in Nutrient Reducing Prairie Strips
The contour prairie strip could be a valuable conservation tool to reduce nutrient loss from agricultural fields. Previous research has shown that prairie strips eliminate up to 90 percent of surface runoff of nitrogen and phosphorus and reduce concentrations of shallow groundwater nitrate. Further, the roots of these prairie strips fuel the denitrification process, suggesting multiple uses in saturated buffers and marginal lands. Prairie strips can also enhance other ecosystem services, including soil quality restoration, wildlife habitat and resilience to flooding. To optimize the potential value of prairie strips for nutrient reduction, we need applied research focused on improving the chances of successful implementation, improving cost-effectiveness and maximizing multiple ecological benefits.
The objective is to improve the implementation, multifunctionality and cost-effectiveness of prairie contour strips for nutrient reduction by pursuing three lines of research:
- validating the conclusions of a 2015 Nashua study at a different location to strengthen the scientific basis for practice recommendations;
- evaluating fall versus spring plantings on stand establishment, cost-effectiveness and functionality; and
- refining the balanced seed mix strategy in light of the realities of native seed markets, by characterizing the most multifunctional and cost-effective composition of graminoids (grassy herbaceous plants) in a 1:1 grass:forb seed mix designed for prairie strips.
The general approach will use techniques implemented at the field scale, using appropriate equipment (tractor mounted seed drills, mowers) so that results are directly applicable to farm operators and contractors. Experimental field trials at the Tallgrass Prairie Center, Cedar Falls, Iowa, replicates a previous INRC-supported study at a new site with a different soil type and cropping history. A new factor will examine the impact of seeding time. The study consists of a spatially blocked split plot design with three factors (seed mix, mowing, seeding time) and six replicates. We will collect data at the site in August/September 2019 and 2020 and record plant density, cost per thousand plants, and measures of functional and species diversity.
The study will also evaluate the graminoid (grassy herbaceous plants) composition in the 1:1 grass:forb seed mix design now being specified for prairie strips in Iowa. This study will be conducted at the Roadman Farm.
In addition, we will conduct two low-replication screening trials for possible inclusion in fully replicated experiments: first, to continue monitoring establishment between a standard seed mix and a tailored “dry site” seed mix on dry soils (Fayette County); second, to examine the impact of seeding depth on small-seeded species.
As this project concludes, we are able to draw important conclusions about the predictability of ecological outcomes when establishing prairie strips. By repeating a field experiment at different sites and years, we demonstrated that the effects of different prairie reconstruction methods are consistent, and that establishment resulting from implementing these methods is predictable. By using a diverse, grass-forb balanced seed mix and conducting frequent first-year mowing in prairie strips, farmer adopters and policymakers can be more confident that they can reliably produce multifunctional stands of perennial vegetation that can help improve water quality and reduce pollinator decline.
In our investigation of our second research question, were able to show that prairie strips generally establish better when planted in the dormant season. Using both an established experiment at the Tallgrass Prairie Center and a new demonstration area in partnership with ISU STRIPS program, we demonstrated that both spring and dormant seeding produced viable prairie strips, but that dormant seeded strips were more multifunctional. Preliminary results from both sites showed that dormant seeding resulted in higher species richness, increased floral diversity, increased abundance of spring/ fall blooming forbs and cool-season grasses, and improved cost-effectiveness compared to spring seeding. Based on our findings, we recommend farmers and other landowners use dormant seeding when establishing prairie strips that follow seed mix best practices.
For our third research question, we found encouraging initial results that diverse grass composition of grass/forb balanced seed mixes can improve ecological outcomes in prairie strips. We used the new demonstration area in partnership with ISU STRIPS to assess whether graminoid composition in seed mixes (diverse vs. simple) affected native plant establishment and cost-effectiveness. We found that species richness in emerging plantings was the establishment measure most affected by graminoid diversity in the seed mix, where a 16-Grass Mix produced more species than a 5-Grass Mix. Other measures, such as sown species abundance and cost-effectiveness, were not initially affected by the composition of graminoids in the seed mix. While these initial results are encouraging, our study assesses only first-year seedling establishment. The majority of effects from seed mix grass composition are only likely to manifest after three to four years. Follow up monitoring is warranted.
As part of smaller screening trials, we showed how seeding small prairie seeds on the surface improves establishment for those species. Using a pilot experiment established at the Tallgrass Prairie Center, we demonstrated that small-seeded species, which make up a large proportion of commonly seeded prairie species, were roughly twice as abundant in surface-seeded compared to drill-seeded treatments. Surface seeding is a more cost-effective method than drill seeding when using a seed mix dominated by small-seeded species. Based on our findings, we recommend prairie seed mixes be sown with planting equipment that allows large- seeded species to be drilled into the ground while small seeds are placed on the surface (most native seed drills can be modified or calibrated to achieve this).
We also collected and analyzed an additional year of data for a previously established INRC project investigating prairie application on marginal lands.
A more detailed final project report is available at the Tallgrass Prairie website at: https://tallgrassprairiecenter.org/sites/default/files/6512_wapsitechupdate_2021.pdf.
A related -peer-reviewed publication was published, as:
Justin C. Meissen, Alec J. Glidden, Mark E. Sherrard, Kenneth J. Elgersma, Laura L. Jackson. “Seed mix design and first year management influence on multifunctionality and cost-effectiveness in prairie restoration.” Restoration Ecology 2021, 28, No. 4: 807-816. https://onlinelibrary.wiley.com/doi/10.1111/rec.13013
Outreach: Over the course of this project, we successfully reached agricultural and conservation audiences with information that will help reduce the barriers to implementing prairie for nutrient reduction. Despite pandemic shutdowns that cancelled many meetings, we gave seven virtual presentations, reaching approximately 812 individuals. In addition, our website is maintained as a web resource for those in need of technical assistance for prairie establishment. We collaborated with the ISU STRIPS team throughout the project with co-hosted virtual field days as well as providing design and logistics support in the establishment of a new STRIPS nutrient-reduction project at Roadman Farm in eastern Iowa beginning in 2020.