Whole farm conservation best practices aren’t limited to in-field practices like no-tillage, strip-tillage, cover crops and extended rotations. A suite of edge-of-field conservation practices, like those pictured below, can help improve water quality in the state by managing the loss of nitrogen from cropland.
Based on 2012 and 2017 United States Department of Agriculture Census of Agriculture data, approximately 50% of Iowa cropland has subsurface drainage. While this drainage makes it possible to farm previously wet soils, it also carries dissolved nitrogen from farm fields to the streams, rivers, lakes, wetlands, and other surface waters of the state.
Excess nitrogen in water leads to local, regional, and national-level alterations to aquatic ecosystems resulting in decreased water clarity, increased algal growth, and oxygen shortages that cause fish kills and reduce diversity. Excess nitrogen also harms drinkable water supplies. Concentrations above the 10 mg/L NO3-N drinking-water standard established by the United States Environmental Protection Agency are not uncommon in Iowa.
Edge-of-field practices such as treatment wetlands, bioreactors, saturated buffers, and controlled drainage can significantly reduce the amount of nitrate-nitrogen that leaves drainage networks. On average, nitrate-nitrogen is reduced by:
- 52% with treatment wetlands
- 53% with saturated buffers
- 43% with bioreactors
- 32% with controlled drainage
While edge-of-field practices have the potential to remove large amounts of nitrate-nitrogen, there is no one practice that works well at all sites. A combination of appropriate practice implementation and high adoption rates is needed to meet the nitrogen reduction goals of the Iowa Nutrient Reduction Strategy that calls for the reduction of nutrient loadings to the Gulf of Mexico by 45% over the coming decades.
Over the next five weeks, we’ll be exploring different edge-of-field practices and the decision trees to help identify which practice(s) will work best for your system.