Establishing pollinator habitats in vegetative filter strips: a sustainable opportunity for Colorado corn farmers

AWQP project to compare and contrast runoff water quality of irrigation runoff water passing through a vegetative filter strip pre and post establishment of pollinator species in the strip.

To learn more, visit the AWQP website.

Authors:
Erik Wardle, Project manager
Emmanuel Deleon, Technical Lead
A.J. Brown, Agricultural Data Scientist
Christina Welch, Project Coordinator
Troy Bauder, Project Advisor

Table of Contents

• Problem Statement and Opportunity
• Approach
  • Study Site: CSU ARDEC
  • Experimental Method: Establishing Pollinator Species
  • Experimental Method: Field Sample Collection
  • Experimental Method: Data Analysis
• Results
• Conclusion

Problem Statement and Opportunity

Colorado corn producers have long recognized the need to utilize practices that benefit both economic and environmental sustainability. In fact, many Colorado corn growers are already using a diverse set of practices that better match the nutrient needs of the crop, reduce environmental impacts, and increase profitability.

Irrigation and intensive rainfall events can cause surface runoff and deep leaching from agricultural fields resulting in loss of valuable nutrients, nitrogen (N) and phosphorus (P). Non-point sources of pollution like these are being considered as the State of Colorado begins to implement nutrient criteria (Regulation 85) for surface water in addition to continued monitoring of nutrients and pesticides in groundwater.

One best management practice (BMP) for reducing nutrient and sediment loss in surface runoff is the use of vegetative filter/buffer strips (NRCS Conservation Practices Standard no. 393). These are areas of perennial vegetation, planted at the edge of an agricultural field, which can help remove nutrients and sediment from tail water. Filter strips are designed to move runoff water across the strip, filtering sediment and nutrients before the water leaves a field. Potential benefits of VFSs include: reduction of sediment and nutrients and E coli in runoff, improving water quality and potentially increasing soil health.

Although there is a body of research on the effectiveness of filter strips in agronomic systems in the midwest, a lack of information is available in the Intermountain West. Additionally, little research has been done to investigate the potential for pollinator habitats in filter strips. More than 30 percent of our food relies on insect pollination, mainly bee species. The annual value of crops pollinated by wild, native bees in the United States is estimated at $3 billion. Recent research has shown that wild native bees, which number more than 4,000 species in North America, contribute substantially to crop pollination on farms where their habitat needs are met (USDA Biology Technical Note No. 78, 3rd Ed.). As such, it is increasingly important that farmers implement practices to promote habitat for these crucial pollinators.

This pilot project will seek to create a pollinator habitat in an existing filter strip located near Fort Collins, Colorado on a surface irrigated grain corn field. The primary project goal is to investigate the potential of establishing pollinator species in an existing filter strip, and measure the impact it has on the nutrient and sediment removal capacity of the filter strip.

Approach

Study Site: CSU ARDEC

An existing filter strip, approximately 0.25 acres in size, was established at the tail edge of a 5.5 acre field at CSU’s Agricultural Research, Development and Education Center (ARDEC) in 2020 and contained meadow brome and orchardgrass (Figure 1). This filter strip significantly reduced significant issues with sediment runoff, and nutrients. The crop rotation for the study field is corn, pinto beans and winter wheat. The field is furrow irrigated utilizing gated pipe and well water. In 2022, the field will be planted to grain corn utilizing appropriate fertilizer BMPs.

Figure 1. Study field and filter strip layout with automated sampler locations highlighted. A short (90 sec.) video tour of the site can be found here: https://www.youtube.com/watch?v=O2kjEdDUdSU

Experimental Method: Establishing Pollinator Species

For this research study, our team will add known species of pollinator plants to the established filter strip. The team will select a variety of early, mid, and late season pollinator species as noted in CSU Extension Fact Sheet 5.616. Planting the pollinators will occur in early spring (March-April) after a significant rain event and will involve mowing a portion of the filter strip to reduce plant competition for better establishment. The newly planted filter strip may need to be irrigated artificially before the first corn irrigation. If so, this will be accomplished by bringing stock tanks full of water to flood irrigate the strip.

Figure 2. Image of the filter strip with pollinator species established in the vegetative filter strip in 2023.

Experimental Method: Field Sample Collection

Our research team has already installed automated water sampling devices both upstream and downstream of the existing filter strip to measure important water quality parameters (including; Nitrate, Phosphorus, Total Kjeldahl Nitrogen, sediment, OrthoPhosphate, and Total Phosphorous), and thus the effectiveness of the filter strip to reduce the concentration and load of the analytes listed above. Each device consists of a flume to measure water flow, A Teledyne ISCO 6712 portable water sampler, a bubbler to measure water depth, a cellular modem, and a solar-powered battery. During irrigation events, these automated samplers will collect 200 mL water each hour. During storm events, it will sample based on intensity at 200 mL of water per 250 gal of water through the flume.

Our team will take pre, mid, and postseason soil samples in multiple, representative locations from 0-8” depths both in the corn field and the filter strip. These samples will be processed for routine soil fertility. Additionally, we will take postseason deep soil samples (5’ deep) to analyze for potential nitrate leaching and loss below the corn root zone.

Experimental Method: Data Analysis

Data collected during the season will be used to determine the ability of the filter strip to remove pollutants and converted to an efficiency percentage in order to compare the new pollinator filter strip to previous years.

Removal Efficiency % = (Upstream Analyte Concentration (ppm or lbs.))/(Downstream Analyte Concentration (ppm or lbs.))×100

Results

Detailed results can be found in the included word document final report.

Below are a few selected graphs and tables from the report for reference: Figure 2. Bar graph comparing annual average concentrations of nitrogen, nitrate (N-NO2; mg/L), nitrogen, nitrate (NO3-N; mg/L), and total Kjeldahl nitrogen (TKN; mg/L) in the inflow (pink bars) and outflow (blue bars) waters in relation to the vegetative buffer strip established at the study site. Error bars represent the standard deviation of the average.

Figure 3. Bar graph comparing annual average concentrations of orthophosphorous (Ortho-P; mg/L), total phosphorous (P-Total; mg/L), and total suspended solids (TSS; mg/L) in the inflow (pink bars) and outflow (blue bars) waters in relation to the vegetative buffer strip established at the study site. Error bars represent the standard deviation of the average.

Figure 4. Bar graph comparing annual average concentrations of nitrogen, nitrate (N-NO2; mg/L), nitrogen, nitrate (NO3-N; mg/L), and total Kjeldahl nitrogen (TKN; mg/L) in the inflow (pink bars) and outflow (blue bars) waters in relation to the vegetative buffer strip established at the study site. Error bars represent the standard deviation of the average.

Calculating removal efficiency

Using Equation 1 from the Data Analysis section above, removal efficiency (R%) was calculated for analytes where data was available for all three years of the study for accurate comparison and placed in Table 1. Additionally, these analytes (NO3-N, TKN, Total-P, and TSS) tend to be some of the more critical analytes for characterizing runoff water environmental impacts.

Table 1. Calculation of removal efficiency (R%) for NO3-N, TKN, Total-P, and TSS water analytes over the 2021, 2022, and 2023 study years. Also shown are the annual average inflow and outflow concentrations. Standard deviation around each average is shown in parentheses next to the average.

| Analyte | Year | Inflow Concentration Mean (Std), mg/L | Outflow Concentration Mean (Std), mg/L | Removal Efficiency, % | |----------------------------------|------|--------------------------------------|---------------------------------------|----------------------| | Nitrogen, Nitrate (As N) | 2021 | 9.1 (0.58) | 8.4 (0.87) | 8.0 | | | 2022 | 7.7 (0.58) | 6.9 (0.85) | 10.9 | | | 2023 | 7.1 (4.19) | 7.9 (2.6) | -11.5 | | Nitrogen, Total Kjeldahl | 2021 | 1.5 (0.42) | 1.1 (0.16) | 28.5 | | | 2022 | 0 (0) | 1 (0.09) | NA | | | 2023 | 8.7 (0) | 16 (0) | -83.9 | | Phosphorus, Total (As P) | 2021 | 0.2 (0.08) | 0.2 (0.07) | -2.7 | | | 2022 | 2.1 (3.56) | 1.8 (3.45) | 13.7 | | | 2023 | 0.5 (0.2) | 0.2 (0.19) | 59.2 | | Suspended Solids (Residue, Non-Filterable) | 2021 | 157.5 (48.56) | 66.7 (47.11) | 57.7 | | | 2022 | 408 (125.91) | 61.7 (31.95) | 84.9 | | | 2023 | 1021.7 (77.78) | 327.8 (396.03) | 67.9 |

For NO3-N, the R% increased from 2021 to 2022 (8.0 % to 10.9 %) but decreased dramatically in 2023 (-11.5). However, these trends are likely statistically insignificant due to the large standard deviations around each mean, which can also be seen in the previous Figure 2. These results indicate that establishing pollinator strips had very little, to a slightly negative impact on NO3-N filtering capacity within the filter strip.

For TKN, the R% was 28.5 % in 2021, but could not be calculated in 2022 because no TKN was found in the inflow water that year. In 2023, the removal efficiency decreased to -83.5 %, indicating that the filter strip was contributing to TKN water concentrations. However, these results are very uncertain, as the 2023 results only had a single water sample, resulting in a lack of any standard deviation. Because of this, we are not confident in saying that the filter strip is contributing TKN to the runoff water without additional results.

For Total P, the R% increased over all study years (-2.7 % in 2021, 13.7 % in 2022, and 59.2 % in 2023). However, there were significant standard deviations around these means, making the overall trend uncertain. However, these results indicate that establishing pollinator species in the filter strip had little effect to a very positive effect on its ability to reduce total P concentrations.

For TSS, the R% remained relatively steady over all study years after considering the large standard deviations around the average concentrations in inflow and outflow waters (57.7 % in 2021, 84.9 % in 2022, and 67.9 % in 2023). These results suggest that establishing pollinator species did not have a negative or positive impact on the filter strip’s ability to remove sediment from runoff water.

Conclusion

The "Establishing Pollinator Habitats in Vegetative Filter Strips" project, funded by the Colorado Corn Council and conducted by Colorado State University's Agriculture Water Quality Program (AWQP), has provided valuable insights into sustainable agricultural practices for in Colorado. This initiative aimed to investigate the impact of pollinator species on the nutrient and sediment removal capabilities of vegetative filter strips in surface runoff water quality.

Our data analysis, utilizing inflow and outflow water samples collected over three years (2021-2023), revealed significant findings regarding the effectiveness of these filter strips. We employed techniques to calculate the removal efficiency of various analytes, including Nitrogen, Phosphorus, and soil erosion (i.e., Total Suspended Solids), thereby assessing the filtering capacity of the vegetative buffer strip. Results indicate that the introduction of pollinator species within the filter strips has varying effects on water quality parameters. Notably, Total Phosphorus and Total Suspended Solids showed a return to near-normal or better than previous levels in 2023 after the full establishment of pollinator species, underscoring the potential benefits of such ecological interventions. However, the impact on Nitrogen forms was less definitive, due to their increased solubility.

One of the critical learnings from this study was the importance of proper seedbed preparation and timely irrigation for the successful establishment of pollinator species. The challenges encountered in 2022 due to competition from existing grass and dry conditions highlighted the need for a well-planned approach to ensure effective establishment and growth of pollinator species. The adaptive measures taken in 2023, including rototilling and the introduction of cover crops, significantly improved the establishment process.

In conclusion, these findings demonstrate that establishing pollinator habitats within vegetative filter strips can be a feasible and beneficial practice for Colorado corn farmers, enhancing both ecological and agricultural sustainability. The lessons learned provide valuable guidance for future efforts in similar contexts, advocating for a balanced approach that considers both agricultural productivity and environmental stewardship.

The AWQP recommends further research to refine the techniques and practices for establishing pollinator species in filter strips, focusing on the nuanced interactions between agricultural practices and ecological enhancements. Additionally, future work could characterize pollinator fauna presence after plant establishment. As the State of Colorado continues to implement nutrient criteria for surface water, such practices could play a significant role in achieving sustainable agricultural goals while simultaneously protecting water quality.

Acknowledgements

The CSU AWQP would like to thank the Colorado Corn Council for their support in this study, especially by providing a no-cost extension so that quality data could be collected for robust conclusions. Additionally, we acknowledge the support of the Colorado State University (CSU) Agriculture Research, Development and Education Center (ARDEC) and Agricultural Experiment Station (AES) for providing the research site and farm management around the study area.

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