Controlled Drainage as a Targeted Mitigation Measure for Nitrogen and Phosphorus

Area of Science:

• Agricultural Science
• Environmental Science
• Water Resource Management

Background:

• Agricultural drainage systems can increase nutrient and water runoff into surface waters, impacting water quality and potentially causing eutrophication.
• Mitigation strategies are needed to reduce nutrient loss from agricultural fields.

Purpose of the Study:

• To evaluate the effectiveness of controlled drainage in reducing nutrient losses during winter crop cultivation in a temperate climate.
• To assess the impact of controlled drainage on groundwater levels, drain flow, and water quality.

Main Methods:

• A 3-year study (2012-2015) on four loamy soil field plots using a before-after control-impact design.
• Controlled drainage was implemented at regulation levels of 50 cm and 70 cm above conventional drain pipe levels.
• Measurements included groundwater levels, drain outflow, nutrient concentrations (N and P), and denitrification rates.

Main Results:

• A regulation level of 70 cm significantly elevated groundwater levels, reducing drain outflow by 38-51%.
• Nitrogen (N) and Phosphorus (P) losses decreased by 37-54% and 43-46%, respectively, compared to conventional drainage.
• Denitrification in the root zone was not significantly enhanced, except on limited occasions.

Conclusions:

• Controlled drainage at a 70 cm regulation level is effective in reducing N and P losses in temperate climates.
• Potential trade-offs, such as increased groundwater nitrogen loss, require further investigation before widespread implementation in regions like Denmark.