Quantifying the Impacts of Planting Cover Crops as a Conservation Tool to Reduce Nutrient Loss from Midwestern Farms

View the project final report

Commodities

Practices

• Crop Production: cover crops
• Natural Resources/Environment: water quality
• Production Systems: agroecosystems

In the Midwestern US, subsurface tile drainage systems facilitate the transport of excess fertilizer nutrients like nitrogen (N) and phosphorus (P) to adjacent streams, where they are then transported downriver causing numerous environmental problems including contaminated drinking water, algal blooms, and subsequent hypoxic “dead zones” after the blooms die and decompose. Planting cover crops is a conservation tool that can be used to reduce N and P loss via tile drains by retaining excess N and P on agricultural fields during Winter and Spring when fields are normally bare. The goal of this project was to quantify the water quality benefits of implementing cover crops at the watershed-scale. Cover crops were planted on ~70% of croppable acres in the Shatto Ditch Watershed (Kosciusko Co., IN). We collected water samples from tile drain outlets and stream sites every 14 days in order to accurately determine how cover crops reduce nitrogen and phosphorus exports from agricultural fields. We communicated our results to potential adopters/promoters of cover crops by attending meetings and field days with the goal of facilitating adoption of large-scale cover crop implementation throughout the region. We evaluated the progress of our water quality monitoring by continuously conducting water chemistry analysis, data processing, and meetings with our partners. The outcomes of this project provide quantitative data about the water quality benefits of cover crops to farmers and resource managers. 

Introduction:

Over the past 150 years, much of the Midwestern United States has undergone extensive land use changes as vast wetlands and prairies have been converted to productive cropland.  However, the tile drainage systems that keep soils dry and maintain productive agriculture also significantly impact adjacent stream channels.  Excess fertilizer nutrients like nitrogen (N) and phosphorus (P) enter streams via tile drains and are then transported downriver causing numerous environmental problems including contaminated drinking water, downstream algal blooms, and subsequent hypoxic “dead zones” after the blooms die and decompose.  For example, reported drinking water violations for excess N have doubled in the last decade and created high-profile news stories like those from Toledo, OH and Des Moines, IA.  Additionally, >50% of the excess N runoff that is causing the recurring dead zone in the Gulf of Mexico has been linked to fertilizers applied to row-crop agriculture in the Midwestern US (Alexander et al. 2008).  In order to reduce non-point source pollution draining from row-crop agriculture to downstream streams and rivers, we need to effectively prevent nutrient loss from fields at the watershed scale.

The planting of cover crops as a landscape-level best management practice is gaining popularity in the North Central Region. According to the most recent SARE Cover Crop Survey Report, cover crop adoption and acreage has increased dramatically in recent years (CTIC 2016). Historically, cover crops have been planted after cash crop harvest to reduce soil erosion, decrease soil compaction, increase soil organic matter, and suppress weed growth (Lal et al. 1991). Cover crops also provide an additional benefit to water quality. Cover crop growth during winter and spring, when fields are normally bare, immobilizes excess N and P in the soil reducing N and P export toadjacent streams and ditches (Ranells and Wagger 1997). Previous research at the field-scale has shown that cover crops can significantly reduce nutrient export from tile drainage in agricultural fields (Kaspar et al. 2007).  However, few studies have linked the implementation of watershed-scale BMPs such as cover crops to improvements in stream water quality. The objective of this project is to quantify the water quality benefits of implementing cover crops at the watershed-scale.

References:

Alexander, R.B., Smith, R.A., Schwartz, G.E., Boyer, E.W., Nolan, J.V., and Brakebill, J.W. 2008. Differences in phosphorus and nitrogen delivery to the Gulf of Mexico from the Mississippi River Basin. Environ. Sci. Technol. 42: 822-830.

Conservation Technology Information Center. 2016. Report of 2015-2016 Cover Crop Survey. Joint publication of the Conservation Technology and Information Center and the North Central Region Sustainable Agriculture Research and Education Program.

Kaspar, T.C., Jaynes, D.B., Parkin, T.B., and Moorman, T.B. 2007. Rye cover crop and gamagrass strip effects on NO³ concentration and load in tile drainage. Journal of Environmental Quality 36: 1503-1511.

Lal R., Regnier, E., Eckert, D.J., Edwards, W.M., and Hammond, R. 1991. Expectations of cover crops sustainable agriculture. pp.1-11. In W.L. Hargrove (ed.) Cover crops for clean water. Proc. Int. Conf., Jackson, TN. 9-11 Apr. 1991. Soil and Water Conserv. Soc. Am., Ankeny, IA.

Ranells, N.N. and Wagger, M.G. 1997. Nitrogen-15 recovery and release by rye and crimson clover cover crops. Soil Sci. Soc. Am. J. 61: 943-948.

Learning Outcomes: Quantify the water quality benefits of watershed-scale planting of cover crops

• In general, we found that tile drains from fields without cover crops had higher nitrate and phosphorus concentrations than tile drains from fields without cover crops. This indicates the potential for cover crops to significantly reduce nitrate and phosphorus export from tile drains.
• We also found a relatively strong correlation between tile drain export and watershed export that indicates reducing tile drain N and P inputs will have a positive impact on water quality in the watershed and reduce nutrient export downstream.

Action Outcomes: Disseminate the results of the project to a wide audience using the education and outreach framework established in our USDA Conservation Innovation Grant (CIG) project and continued with our USDA Regional Conservation Partnership Program (RCPP) project

• We used our established network of partners to reach a large audience of local and regional stakeholders. We attended and presented at numerous meetings, field days, and conferences that increased the visibility of the project and will hopefully promote adoption of large-scale cover crop planting throughout the Midwest.