Evaluating nitrogen losses, soil physical properties, and biological indicators in artificially drained fields in Northwest Minnesota

Abstract

Subsurface drainage is a common practice to improve agricultural production in fields with poorly drained soils. This practice is becoming increasingly common in the Upper Midwest and NW Minnesota, where changing precipitation patterns are generating an increased need for artificial drainage systems. These systems increase yields, and over time, can reshape the soil ecosystem. By changing soil moisture throughout the profile, drainage can alter microbial activity and soil physical properties. In the first chapter of this study, we examined how drainage installation altered N cycling, which is largely mediated by soil microbes. In the two years following subsurface drainage installation, we observed several differences between the drained and undrained treatments: soil nitrate concentrations (NO3-), nitrous oxide (N2O) emissions, N mineralization, and edge of field losses. In the second chapter, we examined the longer-term changes facilitated by drainage to physical and soil health properties by sampling six sites. Three of these sites had their most recent drainage system installation before 2005; the remaining three had installations since 2015. The fields with older drainage systems had increased saturated hydraulic conductivity (Kfs) rates and increased biological activity (potentially mineralizable carbon, water-extractable organic carbon, and water-extractable organic nitrogen). Together, both studies identify the importance of understanding how drainage systems alter the soil ecosystem and demonstrate the importance of understanding drainage as an on-farm management decision. Additionally, they point to a need for more long-term drainage studies which focus on a wider range of soil properties.