EXAMINING SHORT TERM DRAINAGE IMPACTS TO SOIL PROPERTIES IN HYDRIC AND NON-HYDRIC SOILS OF SOUTHERN MINNESOTA

Minnesota, the “Land of 10,000 Lakes”, has a complex glacial history with a landscape characterized by thick accumulations of clay-rich till and widespread areas of relatively low-relief hummocky topography. Prolonged periods of standing water in closed basins formed vast areas of wetlands and hydric soils. Minnesota has been an agricultural leader since the late 1800s and is currently one of the top producers of corn and soybeans in the nation. Tile drainage is commonly used to remove excess water to allow for earlier planting and to aerate the root zone, resulting in higher crop yields. Alterations to soil climate, hydrology, and biota due to drainage can result in pronounced changes to soil physical, biological, and chemical processes and properties. This study examines short-term subsurface drainage impacts to hydric and non-hydric soil properties in southern Minnesota.

Fieldwork was conducted in March 2024 at FarmAmerica, an experimental farm in Waseca County, Minnesota. Multiple soil-sediment cores were collected 1 m deep from three soil series (two hydric and one non-hydric) in five adjacent fields all in long-term conventional corn-soybean rotations. Four fields had tile drains installed in 2022 and one has remained undrained. Cores were described in detail and analyzed for whole-core magnetic susceptibility in 1-cm intervals. Cores were subsampled in 10-cm intervals and combined to create composite samples for each soil series in each field. Soil properties such as aggregate stability, bulk density, particle size, cation exchange capacity, pH, and nutrient, organic matter, and salt content were determined from composite samples.

A range of properties responded rapidly to drainage. Hydric soils lost ~1.1% organic matter after 2 years of drainage, resulting in a net loss to the atmosphere of >150 Mg C/ha from the upper meter of soil, while non-hydric soils changed little. Iron content in non-hydric soils increased nearly three times following drainage, resulting in a considerable increase in magnetic susceptibility, while hydric soils changed little. Non-hydric soils also had a pronounced decrease in pH and increase in nitrogen and phosphorus content following drainage. Given the prevalence of tile drainage in Minnesota and the upper Midwest, it is important to consider the impacts of tile drainage on soil health and the climate in addition to water quality.