Research Update: Controlled Drainage: A drainage conservation practice to reduce phosphorus loss from subsurface-drained fields
By: Dr. Ehsan Ghane, Michigan State University
Dissolved reactive phosphorus (DRP) is the form of phosphorus that is readily available for algae, and too much of it can cause harmful algal blooms in surface water. Therefore, it is important to reduce the transport of excess DRP in drainage water from agriculture fields. Controlled drainage is a conservation drainage practice that can alleviate this water quality issue. In this system, the outlet elevation of the drainage system is managed to limit drainage discharge, which can reduce nutrient loss from the field.
Two on-farm sites in Michigan have controlled drainage systems installed and both sites have been fully instrumented to collect water flow and water quality data (Figure 1). Preliminary results show that a controlled drainage system has great potential for reducing drainage discharge and nitrate load, but more data is necessary to assess the phosphorus-reduction benefit of controlled drainage.
This year, the crop is soybean following the soybean of the previous year due to fertilizer complications in 2022. Water flow rate has been measured and water samples and been collected throughout the growing season. Unlike the extended no-flow condition of the previous year (2021; due to minimal precipitation), there was considerable flow from fall 2021 through spring 2022. The largest flow events occurred in October 2021 and February 2022. Following a strong June flow event, rainfall in the summer of 2022 has been minimal, thereby causing no-flow conditions July. Typically, drainage discharge will resume in October as the crop is harvested and evapotranspiration decreases, tipping the water balance toward drainage discharge. These data are critical for analyzing the effectiveness of controlled drainage.
When asked about the value of controlled drainage research to Michigan corn farmers, Dr. Ehsan Ghane said, “showing the effectiveness of controlled drainage in reducing phosphorus loss from agriculture fields will bring about opportunities to voluntarily improve water quality, and thereby minimizing the chance of nutrient regulations on Michigan producers.”
Next steps: This is the fourth year of funding for this research project. Upon completion, data from all years will be analyzed for trends and the results will be published in the CMPM annual research report, which will be released in early 2023.
Figure 1: Research technician, Samantha Smith, collects water samples from an observation well to find out the nitrate and phosphorus concentration in the shallow groundwater.
