Edge-of-Field
Edge-of-field practices play a crucial role in meeting the Iowa Nutrient Reduction Strategy goals of improving water quality through reducing nitrogen and phosphorus in Iowa's water bodies. Edge-of-field practices involve drainage water management, bioreactors, buffers, saturated buffers, denitrifying wetlands, terraces and sediment control.
Ten Ways to Reduce Nitrogen Loads from Drained Cropland in the Midwest - publication by Illinois Drainage Research and Outreach Program that highlights practices designed to reduce nitrogen loads from cropland.
Bioreactors
Tile-drained water is routed to woodchip filled trench located in a grassed buffer where the tile drainage leaves the field. Once the water enters the bioreactor, denitrification begins. Bacteria use the carbon from the woodchips as a food source and the incoming nitrate for their respiration process. Bioreactors can reduce nitrate levels by 15-60% in tile-drained water.
Wetlands
Wetlands are characterized as having water at or near the soil surface during at least part of the year, containing hydric soils, and containing plants that are adapted to wet conditions. These characteristics provide a great environment for denitrification. Wetlands are shallow in depth and allow the water to slow down and deposit sediment. On average, wetlands can reduce nitrate levels by 40-90%.
Saturated Buffers
Tile drainage water is directed into lateral drainage tile installed parallel to a riparian buffer. The water moves across the length of the buffer removing nitrate. The microbes living in the saturated zone use the nitrate in the water as part of their respiration process. Plants in the buffer also remove nitrates from the drainage water through root uptake. Saturated buffers can remove, on average, 50% of the nitrates in subsurface flow.
Structures
Farm ponds, grade stabilization structures, oxbow restoration, buffers, terraces and sediment control structures are designed to settle sediment and sediment-bound N and P, along with retaining nitrate-N and dissolved P. These practices also provide wildlife habitat, sequester carbon, reduce greenhouse gas emissions, stabilize stream banks, and potentially reduce flood impacts.
Edge-of-Field Resources
Additional Resources: Drainage Water Management
Drainage water management is the practice of using a water control structure in a main, submain, or lateral drain to vary the depth of the drainage outlet. The water table must rise above the outlet depth for drainage to occur.
Drainage Water Management for the Midwest
Drainage Water Recycling for Crop Production and Water Quality in Iowa
Giving Clean Water the Edge: DEVELOPMENT-STAGE PRACTICES
