Complementary practices help buffers outperform expectations in new field research at Michigan State University. 

New research from Michigan State University (MSU) reveals that saturated buffers improve water quality more than originally anticipated, significantly reducing nitrate load by 66% compared to standard tile drainage systems.

Ehsan Ghane, MSU associate professor and Extension specialist, shared insights gained from real-world installations of saturated buffers during an Iowa Learning Farms webinar last week. He discussed how saturated buffers reduce nitrate loss and emerging buffer best practices for design, management and water quality outcomes.

“We’ve learned much from field deployments of saturated buffers that may change how people think about them,” said Ghane, explaining that researchers are gaining a better understanding of when saturated buffers work best and what factors improve their real-world performance.

“Saturated buffers are one of the practices that can significantly reduce nitrate loads.”

Ghane’s research suggests that edge-of-field systems can deliver more consistent nitrate reductions than originally expected, even under variable field conditions. While performance still depends on site-specific factors like soil and hydrology, the findings indicate these practices can reliably reduce nitrogen losses when properly designed and matched to the landscape.

 

Complementary practices

Saturated buffers represent a targeted approach that integrate engineering design with natural soil processes to improve downstream water quality while maintaining productive agricultural land. A saturated buffer system works by combining three processes: 

• Controlled drainage, which manages how much water leaves the field through tile drains.

• Subsurface buffer flow, which treats the water as it slowly moves through the soil. 

• Buffer strip, which helps reduce and treat surface runoff and absorb nutrients from the subsurface buffer flow.

The practices are complementary to each other, Ghane said, with each being an effective nitrate reduction tool on its own but providing higher success when utilized together.

His research found several surprising results. For example, the controlled drainage component actually reduces nitrates by as much as 53% alone, which was more than expected, he said. When adding the subsurface buffer flow component to the system, that effectiveness increases to 66%, he said.

“The whole system tends to be more beneficial than just one component,” Ghane said.         

The effectiveness of saturated buffers depends on site-specific conditions, including soil characteristics, hydrology, buffer width and the proportion of tile drainage water that can be safely redirected. While they don’t eliminate all nitrate losses, they can substantially reduce the amount that reaches surface water when properly designed and installed.

A key advantage of saturated buffers is that they require relatively modest changes to existing drainage infrastructure. In many cases, installation involves adding a distribution control structure near a tile outlet rather than redesigning an entire drainage system.

This makes them more accessible compared to more intensive structural changes in field drainage design.

“We found evidence that saturated buffers are effective on fields with slopes of 1% or greater, contrary to the previous assumption that a minimum 2% slope is required,” Ghane said.

Also, “field data showed that when ditch water levels rise and fall similarly to the buffer water table, streambank instability is unlikely, suggesting that existing depth restrictions for saturated buffer pipes may be overly conservative,” he added.

Ghane emphasized that conservation drainage practices must be matched carefully to local conditions and the landscape.

In addition to environmental benefits, saturated buffers are often supported through cost-share programs, helping offset installation expenses for farmers. Their performance has made them an important component in broader water quality strategies across agricultural watersheds, Ghane said.