Beyond the outlet: How lateral seepage shapes controlled drainage performance in a sandy soil

Controlled drainage (CD) is used in temperate humid regions to reduce water and nutrient losses. Although CD effectiveness has been widely evaluated, the role of lateral seepage in sandy soils remains underexplored and neglecting it may overestimate reductions in water and nutrient losses. The objective was to evaluate CD performance in a sandy loam field prone to lateral seepage and quantify how lateral seepage alters estimates of water and nitrate losses from the field. A paired-field approach was used to quantify the apparent performance of CD based solely on drainage outlet measurements. Actual performance, defined as losses through the drainage outlet plus lateral seepage, was then estimated by integrating DRAINMOD simulations with field observations. The paired-field analysis showed that CD significantly ( p- value