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How do soil properties evolve over time in subsurface-drained fields?

Former CFANS graduate students Aaron Frankl (left) and Kyle Sherbine soil sampling “Minnesota’s Coolest Drainage Plots” at the Northwest Research & Outreach Center in Crookston.
By: Lindsay Pease, Extension nutrient management specialist

It is well known that installing a subsurface drainage system can help to remove excess water from farm fields. Installing a subsurface drainage system is a long-term decision that provides long-term benefits. That is why back in October 2019, I initiated a new subsurface drainage project at the Northwest Research & Outreach Center in Crookston. The overall goal of “Minnesota’s Coolest* Drainage Plots” (*by annual average temperature) is to explore the short- and long-term impacts of subsurface drainage systems in northwest Minnesota.

This project has served as a jumping off point for other research questions about subsurface drainage systems. One such question was initiated by Aaron Frankl while he was pursuing a graduate degree in Land and Atmospheric Science. Frankl identified a gap in the literature on how soil properties change over time in subsurface-drained fields. Because he did not want to wait 20 years to finish his graduate degree, we came up with a research project that could shed light on this question (with research support from both the Minnesota Corn Research & Promotion Council and AFREC – Minnesota’s Agricultural Fertilizer Research and Education Council).

To answer this question, we identified six subsurface-drained fields in northwest Minnesota and grouped them into two categories. Three were drained more than 15 years ago and three were drained in the past five years. We also added one undrained field to the study as a control. We collected a suite of soil physical and biological properties at each field to see what differences we could find between older and newer sites.

We found that soil physical properties evolve over time in subsurface-drained fields. Saturated hydraulic conductivity (the speed with which water can flow through the soil when it is completely water-logged) was greater at the older sites. Soil structure is impacted when a drainage installation takes place. This shows it may take five years or longer for the soil to fully recover its structure following installation.

Soil biological indicators also shifted over time in subsurface-drained fields. Older sites tended to have greater amounts of water extractable organic nitrogen and water extractable organic carbon in the soil. This means that there was more nitrogen and carbon readily available for microbes to consume. This further supports our hypothesis that it may take a few years for soils to recover following subsurface drainage installation.

The broader importance of this study is that it shows that drainage status is not a simple “yes” or “no.” Subsurface drainage systems dynamically change soil properties as they age, and these changes are generally positive for creating a healthy soil environment. We plan to continue monitoring our new drainage installation at the NWROC over time to see if our findings hold true as our system ages.

For more information on this study, you can check out the full research article here: Comparing the short- and long-term impacts of subsurface drainage installation on soil physical and biological properties


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