Saturated buffers: Protecting water quality, one field at a time

Agricultural fields are an unintended contributing factor to the amount of nitrate-nitrogen entering Illinois’ waterways. Excess nutrients, like nitrate-N, impact our state’s water quality and the water quality downstream. According to the Illinois Nutrient Loss Reduction Strategy, an average of 10 pounds per acre of nitrate-N is lost annually and ranges from 0.7 pounds to 42 pounds per acre per year. Agricultural conservation practices are designed to keep the nutrients in the field where they belong or capture the nutrients before they enter local water bodies to protect water quality.

Saturated buffers are an edge-of-field agricultural conservation practice and are one of the newer practices that have been adopted by the NLRS. Saturated buffers became an approved practice in the 2021 Biennial Report due to the number of studies submitted with the practice proposal, their geographic relevance, and the quality of work.

A saturated buffer is a vegetated buffer with lateral tile lines installed parallel to the drainage outlet. Tile-drained water is diverted through a water control structure into the lateral perforated pipes. As water drains into the buffer, the living roots of perennial vegetation take up the water and nutrients, specifically nitrate-N. Nitrate-N in tile water is also converted to nitrogen gas through denitrification.

While saturated buffers can reduce nitrate-nitrogen leaving a field, it is not suited for every tile outlet. Saturated buffers typically treat a drainage system from a single field on 6– to 12-inch mains. There also needs to be at least a 30-foot vegetative buffer between the field and the outlet ditch with at least 1.2% organic matter in the top 2.5 feet. The banks of the outlet ditch must be stable, and it works best where the outlet is lower than the contributing field.

Saturated buffers decrease the amount of nitrate-nitrogen being discharged into local waterbodies from fields. The NLRS Ag Water Quality Science Team gave the practice a 40% nitrate-N reduction value, the median value of the 27 site years selected for inclusion in the team’s assessment. No phosphorus reduction value is associated with the practice.

Decreased turbidity and volume of water in waterways is another potential outcome of a saturated buffer installation. Saturated buffers also require little annual maintenance and will stabilize stream banks. The vegetative buffer also provides wildlife habitat.

While there are many benefits to saturated buffers, there are also some considerations to take into account. During high flow events or extremely wet years, the system does contain a bypass system to make sure water isn’t being backed up into the field, which means there could be water that the saturated buffer won’t treat. It also requires a long vegetative buffer along the ditch or stream. The soils in the buffer must be relatively high in organic matter and low in sand or gravel. The stream banks must also be stable.

To learn more about this practice, you can watch the “What is a Saturated Buffer?” video by going to go.illinios.edu/SaturatedBufferDemo. To learn more about other agricultural conservation practices, visit Illinois Extension’s nutrient loss reduction website at go.illinois.edu/NutrientLoss.

Rachel Curry is a University of Illinois Extension agricultural and agribusiness educator and is part of Illinois Extension’s Nutrient Loss Reduction Strategy implementation team.