Saturated Buffer Strips: Drain, Sustain & Gain
The Agricultural Drainage Management Coalition (ADMC), Agricultural Drainage Management Systems Task Force and Dr. Dan Jaynes with the National Laboratory for Agricultural & The Environment collaborated to demonstrate and evaluate saturated buffers at field scale to reduce nitrates and phosphorus from subsurface field drainage systems.

With many of the row-crop agriculture fields in the Midwest being located adjacent to ditches, streams, rivers and lakes, it is no surprise that nutrient transport from agriculture lands is a major concern. Large areas of the Midwest are intensively tile drained and it is assumed that many of the vegetated buffers adjacent to waterways are being under-utilized, because the tile outlets quickly move large amounts of subsurface flow past the buffer and into the receiving waterway without any opportunity for treatment by the buffer.

The project collaborators sought to demonstrate and evaluate the effectiveness of a new conservation practice commonly referred to as a Saturated Buffer (SB). The goal of a SB system is to hydrologically reconnect a subsurface drainage outlet with an edge-of-field buffer. This practice takes advantage of both the denitrification and plant nutrient uptake opportunities that are known to exist in buffers with perennial vegetation as a way to remove nutrients from the drainage water.
The first demonstration monitored 15 sites across the Midwest from September 2012 to September 2015. The overall conclusion was that when proper site conditions and design considerations are met the Saturated Buffer practice can be an effective method for reducing nitrate transport from subsurface drainage systems. Further highlights regarding the project, as well as a full copy of the report, can be found below.

This material is based upon work supported by the United States Department of Agriculture, Natural Resources Conservation Service (69-3A-75-11-205) and the Farm Service Agency (AG-3151-P-15-0168). Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the U.S. Department of Agriculture.

The second demonstration sought to quantify the effectiveness of installing saturated buffers on a conservation reserve program to reduce nutrient loading from tile drainage waters. 9 saturated buffers in Iowa, Illinois, and Minnesota were monitored from September 2016 to April 2017. These sites intentionally included a variety of soil types, buffer vegetation, surface topographies, and ditch/stream channel depths.

All 9 sites were consistent in showing nitrate concentration reductions from the main line of the drainage system to the stream side test well. This reinforces data from the previous work where 27 out of 28 field years indicated the same reductions. Current data collection techniques heavily support the use of saturated buffers as a credible nitrate load reduction practice. The cost per pound of nitrate removed is low compared to other nitrate removal practices.

The third demonstration built off of the first and second projects and aimed to further quantify the effectiveness of saturated buffers in reducing nutrient loading from tile drainage waters. 7 sites were monitored throughout Iowa, Illinois and Minnesota from October 2017 - August 2018. The seven saturated buffers had an average nitrate-N concentration reduction ranging from 41-97% during the monitoring period. Nitrate load reductions ranged from 10 - 194 pounds.

ADMC also contracted with the Department of Crop Sciences from the University of Illinois, Urbana-Champaign to develop a decision support tool to identify sites that will likely provide cost-effective locations for saturated buffer installations in the Midwest. This step-wise model revealed a conservative estimate of 46,920 miles of cumulative stream bank suitable for saturated buffers.

The developed decision support tool exhibited that saturated buffers could potentially be installed to treat nearly 9.5 million acres of tile-drained Midwest land and remove 5% to 10% of the tile contributed nitrate-N load or 2-5% of the overall load delivered to the Gulf of Mexico. Enhancing a standard buffer with a saturated buffer where possible could remove approximately thirteen times the annual amount of N, while making the practice six to ten times more efficient in terms of $/lb. of N removed.

Project 3: (August 2018) Quantifying the Effectiveness of Saturated Buffers to Reduce Nutrient Loading from Tile Drainage Waters
Project 2: (April 2017) Quantifying the Effectiveness of Installing Saturated Buffers on Conservation Reserve Program to Reduce Nutrient Loading from Tile Drainage Waters
Project 1: (December 2015) Demonstrate and Evaluate Saturated Buffers at Field Scale to Reduce Nitrates and Phosphorus from Subsurface Field Drainage Systems
To accomplish the goals of this demonstration project, fifteen monitoring sites were selected in four different states (IA, IL, IN, and MN). A variety of site characteristics, not all considered "ideal", were chosen to demonstrate the effectiveness of the practice if implemented at a large scale. This also afforded the opportunity to explore why some sites had saturated buffer systems that were more effective at removing nutrients than others. Water flow rates from the subsurface drainage systems were monitored, and water samples for nitrate and phosphorous analysis were taken from September 2012 through September 2015.
The data from this study confirms that, when proper site conditions and design considerations are met, the saturated buffer strip practice can be an effective method for reducing nitrate transport from subsurface drainage systems. Phosphorus loads, however, appear to be generally unaffected by this practice.

The findings demonstrated that the Nitrogen (N) concentrations were less in the buffer than the tile lines in 27 out of 28 field years monitored. Overall the average N concentrations across the buffers indicated substantial N removal in about 17 of the 27 field years. N may have been removed in the other 10 field years as well, but due to inconsistent trends the nitrate removal amount could not be calculated with certainty.

Furthermore, using the costs of installation for the sites that proved effective in removing nitrate, assuming a 50 year effective lifespan for these installations, and a 4% inflation rate or cost of money, the costs ranged from $0.55 to $4.64/lbs-N with an average of $2.13/lbs-N removed. This compares to $1.38/lbs-N for denitrification bioreactors, $5.06/lbs - N for nitrate removal wetlands and $3.21/lbs - N for rye cover crops (tile drained acres). (Source: IL Nutrient Loss Reduction Strategy). Thus, the effective saturated buffers in this study had a cost range similar to these other field edge practices and much less than fall-planted cover crops. In addition, the practice takes no more land out of production than already used for the riparian buffer.

Unlike a bioreactor, which utilizes a woodchip trench to provide a carbon food source for the denitrifying microbes, a Saturated Buffer uses the carbon already present in the soil as the food source. This allows for potentially similar nutrient removal to occur without the cost of digging a large trench and filling it with wood chips. The greatly reduced cost of implementation could prove to be significant in allowing the Saturated Buffer practice to receive widespread implementation.

The Agricultural Drainage Management Coalition (ADMC) is a nation-wide group of agricultural, industry, and environmental interests that have come together to promote drainage water conservation practices. The ADMC includes over 60 key stakeholders, including individual farmers, industry manufacturers, and environmental groups like The Sand County Foundation. ADMC assists the agricultural and environmental communities in improving water quality and increasing yields. They serve as a resource for the latest technologies in drainage water management systems and work at the local and state level to educate farmers, drainage and conservation groups, local, state and federal authorities to build an understanding of the latest drainage water management systems.

The Agricultural Drainage Management Systems Task Force (ADMSTF) is a multi-agency and university collaboration that has met regularly since 2003 to develop a national effort for implementing improved drainage water management practices and systems that will enhance crop production, conserve water, and reduce adverse off-site impacts on water quality and quantity.

The National Laboratory for Agriculture and The Environment generates information, which addresses critical problems in agriculture and watershed management, leading to the development of innovative solutions, which increase the efficiency of agriculture systems and reduce environmental risk. Transdisciplinary teams address this mission through coordinated research addressing problems in abiotic and biotic systems that underpin agricultural and watershed systems.

Download a PDF of the full report.