In addition to cropping and nutrient management strategies to limit nitrate losses and improve nitrogen efficiency, conservation drainage practices include several drainage system modifications and edge-of-field practices for reducing nitrate losses from drainage.
Controlled Drainage (Drainage Water Management)
Controlled drainage (drainage water management) uses flow control structures to manage the amount and timing of drainage by managing the outlet elevation. Draining less water at times when drainage is not critical results in reduced nitrate loss.
A bioreactor is a trench filled with wood chips that drainage water is routed through. Denitrifying bacteria in the wood chips convert nitrate in the drainage water into inert nitrogen gas, reducing the amount of nitrate delivered to the outlet.
Saturated buffers use a control structure to divert drainage water and raise the water table within a riparian buffer. Water flows through the soil in the buffer, where it has a chance to interact with plants and microbes in the buffer for nitrate removal.
Nitrate concentrations can be reduced by routing drainage water through a wetland, which also provides wildlife habitat and other benefits. Nitrate reductions result from plant nutrient uptake, microbial immobilization, and denitrification.
Drainage Water Recycling
Drainage water is captured in a holding pond or reservoir and used for irrigation in the summer. Drainage water recycling increases yields from the irrigation benefit, and the nitrate in the drainage water is reduced or recycled.
In shallow drainage, the drains are installed at shallower depths (2.5-3 feet) instead of typical depths (4 feet or more). Shallow drains remove less water, which reduces nitrate losses.
Christianson, L.E., J. Frankenberger, C. Hay, M.J. Helmers, and G. Sands, 2016. Ten Ways to Reduce Nitrogen Loads from Drained Cropland in the Midwest.
Pub. C1400, University of Illinois Extension.
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