Function Surface and subsurface flow o erosion mitigation Sedimentation o phosphorus Denitrification
Bio-reactant Filtration Functional properties Construction Long term maintenance
Function of bio-reactors Contained biological processes o removal targets Aerobic and Anaerobic Simple example o Denitrification o Sedimentation
Construction Two stage containment system o First stage prevents overflow o Second stage filters drainage Inputs o Sand o Carbon source woodchips compost o Bacteria obtained from river sediment
Controlled Drainage Keeps water table high during the off-season Increased rate of denitrification
Subirrigation Irrigations back through subsurface drain tiles used during dry periods
Management of Controlled Drainage/Subirrigation Farmer needs to know: 1. when to raise/lower the control structure 2. at what height to maintain the weir in the control structure 3. when to add water to the system Depends on: specific site, crops, soil type, drain depth, etc.
Seeding of Crop Fields for Winter Months Maintains root integrity year round Plants are able to take up phosphorus when storm events occur especially useful in clay and silt dominant soils Can produce additional crop yields Improves soil condition for next growing season *** Cost effective compared to fallow field maintenance Legumes such as Hairy Vetch and Subterranean Clover improve soil quality by fixing Nitrogen (http://boyneriver.org/wp-content/uploads/Hairy-Vetch_Web-jpg.jpg) (http://www.mccc.msu.edu/images/covercrops/kura_clover.jpg)
Cover Crops for Vermont Winter Rye Can germinate at 33 degrees F Scavenges residual N from previous crops Can be grown with Hairy Vetch Field Pea (Legume) ●Winter kill-crop ●Planted in August/September ○reaches maturity before first frost ●Dead plant material shieds soil and roots remain underground
Optimal Spacing Prior to Installation The less dense the drains, the lower the amount of leached nitrogen Closest distance → 20 meters Closer than that and crop yield decreases and nitrogen runoff increases
Optimal Drain Depth Prior to Installation A decrease in drain depth from 1.5 to 0.9m decreased Nitrogen losses by 14% o Little change when deeper than 1.2 meters o Water has drained Shallower drains not examined o Could impede root growth and water absorption
Fertilizer Application Reducing Nitrogen inputs from: 200 kg ha −1 to 125 kg ha −1 reduced Nitrogen losses by 57% ** NO reduction in crop yields This application rate aligns with recommendations put forth by Waseca, Minnesota, where the study was performed o also aligns with other regional recommendations (http://www.novum-nl.com/webtheek/dscf1714.gif)
At Risk Soil Types 1.Clay soils that easily slake 1.Silty soil with low Organic content o Prone to erosion 3.Sandy soil profiles with low P sorption capacity o Iron and Aluminum in subsoil raise P sorption cap.
Best Management Practices ** NOTE: Often times soils are a mix of sand, silt, and clay The most important objective is to promote a healthy soil profile