Summary prepared by: Ehsan Ghane, Department of Biosystems and Agricultural Engineering, Michigan State University
Ghane, E., AbdalAal, Y., Tehrani, A. (2025). Paired-field evaluation of a saturated buffer reveals significant water-quality benefit through upstream weir management. Agricultural Water Management. 318, 109664. https://doi.org/10.1016/j.agwat.2025.109664
Ghane, E. (2025). Unveiling the true potential of saturated buffers (E3535). Michigan State University Extension Bulletin. www.canr.msu.edu/drainage
Major Findings:
We conducted a paired-field study at an on-farm site in Michigan, USA, comparing a saturated buffer (SB) system to a free drainage control field. Results showed:
- The saturated buffer system significantly reduced nitrate-N load by 54.5% (11.1 kg/ha) annually compared to free drainage.
- The upstream weir of the system, functioning as controlled drainage, was the primary driver behind the annual load reduction, accounting for most of the flow and nitrate-N load reduction.
- High-level weir management (<35 cm weir depth below ground surface at structure) was more than twice as effective as low-level weir management (>35 cm weir depth below ground surface at structure), removing 0.076 kg/ha nitrate-N daily.
Contributions to the conservation drainage community
This study showed that in saturated buffer applications where a three-chamber structure is used, the upstream weir acts as controlled drainage reducing both flow and nitrate-N load in conjunction with the saturated buffer. Actual performance of saturated buffers can easily be underestimated when not acknowledging the functionality of the upstream weir. Using similarly structured paired-field studies in the future may help others explicitly quantify the influence of the entire saturated buffer system, which includes the upstream weir management as well as the flow through the buffer.
It was also clear during this study that even though the water-managed zone upstream of the control structure was only 6.6% of the total drainage area due upstream field slopes, the upstream weir management functioning as controlled drainage reduced nitrate-N load by more than 50% compared to the free drainage field. This suggests that prior assumptions around site suitability for controlled drainage requiring flat fields with slopes generally less than 1% may be overly restrictive, particularly when paired with complementary practices like saturated buffers.
