The Midwest United States is one of the world’s leading soybean-producing regions. According to a 2017 Food and Agriculture Organization report, the region accounts for more than 34% of global soybean production. Over the years, soybean yields have increased steadily thanks to improved genetics and better management practices. While growers can influence genetics and management, weather remains largely out of our control.

Drought during critical reproductive growth stages can cause major yield losses, as many growers experienced this year. On the other hand, excessively wet springs can be just as damaging, leading to delayed planting, poor root development, and waterlogging. The good news is that yield losses from both dry and wet conditions can be reduced with proper water management—irrigation during drought and effective drainage during wet periods.

Although irrigation is often a costly investment and not feasible for all operations, drainage systems are one of the most effective and widely adopted tools for managing excess water. Good drainage improves soil health, allows timely field operations, and prevents prolonged waterlogging. Studies have shown that improved drainage can increase soybean yields by up to 8% (about 4 bu/acre) compared with poorly drained fields.

While surface drainage has been used for many years, subsurface drainage is increasingly recognized as a practical long-term solution. Growers considering subsurface drainage generally have two options: conventional (free-flow) drainage or controlled drainage. Controlled drainage systems use a water-level control structure to regulate how much water leaves the field. This allows producers to remove excess water during wet periods while retaining soil moisture during drier conditions. In addition to improving yield stability, controlled drainage has been shown to reduce nutrient losses and improve downstream water quality.

A multi-state study evaluating controlled drainage systems included 55 site-years across 13 field locations in the Midwest and North Carolina between 2000 and 2017. Overall, the researchers found no consistent yield advantage of controlled drainage compared with conventional (free-flow) drainage in corn production. However, weather conditions played a major role. During mild to moderate drought years, controlled drainage increased corn yield by 4–14% by helping conserve soil moisture. In contrast, during wetter growing seasons, yields were reduced by 4–10% due to excess soil water (Youssef et al., 2023).

Similar results have been reported for soybean. Researchers from the University of Minnesota, North Carolina State University, and the University of Missouri analyzed data from 13 site-years collected between 2007 and 2018 to compare soybean yields under control and conventional drainage systems (Strock et al. 2025). Across all site-years, median soybean yields were nearly identical, 58.21 bu/acre under controlled drainage and 58.00 bu/acre under conventional drainage, indicating no overall yield difference between the two systems.

That said, yield responses varied depending on seasonal conditions. In about 35% of the site-years, soybean yield either increased or decreased by up to 4% under controlled drainage. When researchers focused on a subset of 11 site-years, controlled drainage reduced plant stress during mild to moderate drought and increased soybean yields by 4–8% in six of those site-years. However, during wetter growing seasons, controlled drainage reduced soybean yields by 4–9% in five site-years.

The researchers also examined when soybean plants were most likely to experience stress during the growing season, both by growth stage and by month. Results showed that soybeans were most affected by excess water from planting through the V5 stage, while drought stress was most common around the R4 (pod development) stage. In Figure 2, the smaller bars (at P-V5 and R4) indicate that these stress conditions occur more frequently, suggesting that wet conditions are more likely early in the season, while dry conditions are more likely later during pod development.

The flowering period (R1) appeared to be a transition point between wet and dry conditions. The wide boxplots during this stage show that soybeans can experience either excess moisture or drought during flowering, depending on the season.

On a monthly basis, excess moisture caused the greatest plant stress in May. June represented a transition period from wet to dry conditions, while the remaining months of the growing season were primarily characterized by drought-related stress.

Using a different stress index, the authors found that excess moisture was a greater challenge than drought at only two of the 11 study sites. Even at those locations, drought stress was still present. Overall, these results indicate that drought poses a greater and more widespread challenge to soybean production than wet conditions across most sites.

Based on multiple analyses, the authors developed practical guidelines for switching between controlled drainage and full drainage during the soybean growing season. They recommend using full drainage during vegetative stages to quickly remove excess water, then shifting to controlled drainage at flowering (R1) while closely monitoring rainfall and returning to full drainage when heavy precipitation occurs. Controlled drainage is most beneficial from full bloom through pod elongation (R2–R4) and can continue from beginning seed through pod fill (R5–R6), with adjustments back to full drainage during wet periods. Finally, full drainage is recommended from physiological maturity through harvest maturity (R7–R8) to ensure good field conditions for harvest.

Although soybean yields were not significantly different between full and controlled drainage systems overall, controlled drainage has been previously reported to reduce nutrient losses and helped relieve mild to moderate drought stress in some years. These benefits make controlled drainage an option worth considering, especially in fields prone to late-season dryness. However, managing manual control structures across large farms can be challenging, and sensor-based automated systems may be difficult to justify economically given that yield gains (around 4%) occur only in certain years. In short, controlled drainage is more of a risk-management and water-quality tool than a guaranteed yield booster. For most Kentucky soybean fields, sticking with a free-flow (full) drainage system is likely the best option. Free-flow systems are easier to manage and require less time and investment. Controlled drainage may still help in specific situations, such as drought-prone fields; but for typical Kentucky soils, your soybean field may just like things the old-fashioned way: free-flowing, full speed ahead, and hassle-free.

Sources

Youssef, M.A., Abdelbaki, A, M., Negm, L.M., Skaggs, R.W., Thorp, K.R., and Jaynes D.B. 2018. DRAINMOD-simulated performance of controlled drainage across the U.S. Midwest. Agricultural Water Management, vol (197).

Strock J.S., Youssef, M.A., Moursi, H., Nelson, K., Ranaivoson, A.Z., Poole, C.A. 2025. A synthesis of soybean yield response to controlled drainage under varying precipitation patterns in the US Midwest. Vol (318).

Citation

Shamim M.J., 2026. Is Controlled Drainage Worth the Extra Bucks, Time, and Efforts in Soybean Fields? Kentucky Field Crops News, Vol 2, Issue 01. University of Kentucky, January 16, 2026.

Mohammad Shamim, mshamim@uky.edu