Improving Outcome Predictability, Multifunctionality and Cost-effectiveness in Nutrient Reducing Prairie Strips

Date: 
Aug 2019

Issue

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.

Objective

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.

Approach

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.

Project Updates

December 2019

First-year vegetation sampling was conducted at a newly established field experiment at the Tallgrass Prairie Center in September. This new experiment seeks to validate the conclusions of the team’s 2015 Nashua study at a different location and evaluate fall versus spring plantings on stand establishment, cost-effectiveness and functionality. Measures were taken for plant density, flower density, canopy cover and species richness of three seed mixes planted in either November or April that were mowed or unmowed the first year.

Preliminary analysis shows general correspondence among experiments when comparing the effect of seed mix and mowing. In both studies, mowing and seed mix design influenced stem density. Initial results showed that planting in the dormant season led to better establishment of cool season grasses and sedges, spring forbs and fall forbs. Planting during the growing season resulted in better establishment of warm season grasses and legumes.

First-year vegetation sampling was conducted at a newly established seeding depth demonstration site in September. This new demonstration study examines whether the type or technique of equipment used (broadcast/drop vs. drill) when seeding prairie reconstructions influences establishment. For the many small-seeded prairie species that may have light requirements for germination, this could impact cost-effectiveness and establishment success. Measurements were taken for plant density, cover and species richness of a seed mix dominated by small-seeded species that was sown on the surface or ¼” deep with a seed drill. Preliminary analysis shows that plant density is higher for small-seeded species when planted on the surface.  Planting depth did not appear to be an influence for larger seeded species.

Year two vegetation sampling was conducted at the Wapsi-Fairbank Research Field in August. Plant density continues to be comparable between dry- and mesic-adapted mixes, though the dry-adapted mix produced slightly more spring forbs. Work in upcoming months will consist of further analysis of vegetation measures.

Researchers worked with partner farmers and landowners to plan an upcoming demonstration site that will assess the importance of grass diversity in prairie strips, securing an initial buy-in with landowners and farm managers at the Roadman Farm to establish a new demonstration site as part of the rollout of the new Prairie Strips CRP practice. Because this practice was only unveiled for sign-ups in November 2019, the date of seeding for this new project is planned for fall 2020.

Preliminary results were presented at conferences with agriculture and conservation audiences, including to the Grassland Restoration Network Meeting at the UW Landscape Arboretum Aug. 21, 2019.

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