Evaluation of Controlled Tile Drainage on Limiting Edge of Field Phosphorus Losses in a Clay Soil in a Cold Agricultural Region

Abstract

This study examined edge of field (EOF) discharge and phosphorus (P) losses from a Brookston clay soil in a cold agricultural region over four years and quantified the influence of controlled tile drainage (CD) on seasonal and annual P exports in tile drainage. Annual EOF P losses ranged from 0.38 to 2.15 kg/ha for total phosphorus (TP), and 0.07 to 0.54 kg/ha for soluble reactive phosphorus (SRP) at the freely drained site. The majority of EOF discharge from the freely drained site was through subsurface drainage (66 to 98% annually), but P losses were evenly divided between surface and subsurface losses. At the CD site, CD is only used during the growing season (GS; May to September) at the site. Given the small volumes of flow during the GS, CD reduced subsurface discharge by 3.9% and P losses by 4.4% over the study period. Water table dynamics and subsurface runoff chemistry were not significantly impacted by the practice. The majority of discharge (90.1%), SRP (96.8%) and TP (94.2%) losses occurred outside of the GS, limiting the overall impact of CD at the site. In order to reduce EOF P losses in tile drainage, it is essential that CD is used throughout the year. Understanding the relative contributions of seasonal drainage control on overall annual losses is important to understanding the overall benefit of the practice and improving its application to reduce EOF P losses.