Department of Agricultural and Biosystems Engineering Cover Crops, Wetlands, and Conservation Drainage Matthew Helmers Dean s Professor, College of Ag. & Life Sciences Professor, Dept. of Ag. and Biosystems Eng. Iowa State University
Estimated Nitrate-N Loss, January to June for 1997-2006 Source: David et al., 2010
Gulf of Mexico Hypoxia Goals Hypoxia Action Plan Goal: Reduce the size of the zone to 5,000 km 2 EPA SAB Recommendations: Reduce Total Riverine Nitrogen and Phosphorus Loads by 45%
Is this Primarily a Fertilizer Problem?
Variability in Drainage, Nitrate Concentration and Nitrate Loss Corn-Soybean Rotation 150/160 lb-n/acre Application Rate
Nitrate Response to Nitrogen
Is this Just a Natural Process?
Soil Nitrate Production vs. Crop Nitrate Uptake Rate of soil nitrate production from native soil organic matter Rate of corn or soybean nitrate uptake The majority of nitrate used by corn and soybean comes from soil nitrate production. Corn gets the difference from fertilizer while soybean gets the difference from legume fixation of atmospheric nitrogen. March February In the shaded areas, the soil produces nitrate, but there is no crop to use it. As a result, some nitrate is lost to waterways.
Winter Cereal Rye Cover Crops Ames Gilmore City
Soil Nitrate Production vs. Crop Nitrate Uptake Addition of a Cover Crop Rate of soil nitrate production from native soil organic matter Rate of corn or soybean nitrate uptake Cover crops can use nitrate when corn and beans are not growing, thus reducing the asynchrony between soil nitrate production and crop nitrate uptake. Cover crop nitrate use Cover crop nitrate use March February In the shaded areas, the soil produces nitrate, but there is no crop to use it. As a result, some nitrate is lost to waterways.
Impacts of Cover Crops on Nitrate-N Load in Drainage Water Gilmore City 36% Reduction 34% Reduction
Subsurface Drainage and Nitrate-N Leaching 2010-2013 20 15 10 5 Subsurface Drainage Nitrate-N Concentration 0 Nitrate-N Load Subsurface Drainage (in) Flow-weighted Nitrate-N Concentration (ppm) Annual Nitrate-N Load (lb/acre) 20 20 CORN-soybean SOYBEAN-corn Continuous Corn Continuous Corn with Cover Crop Prairie Fertilized Prairie 15 10 5 15 10 5 0 0
This is Just a Tile Drainage Problem?
Water Flow Pathways Naturally Well-Drained Soils Soils with Poor Natural Drainage Land management and land use impacts ET and infiltration which in turn impact surface runoff, subsurface drainage, deep percolation
What Can We Do?
Nitrogen Management 4Rs
In-field/Land-use Practices
Edge-of-Field Practices
Conservation Drainage
Subsurface Drainage Bioreactor From Christianson and Helmers, 2011 Illustration by John Petersen (www.petersenart.com)
Nitrate Removal Wetland
Iowa Conservation Reserve Enhancement Program (CREP) Targeted Wetland Restoration Corn Soybean DD Tile 1 km W.G. Crumpton, Iowa State University
What Might it Take to Reach our Goals? Example: Combination Scenarios that Achieves N Goal From Non-Point Sources for Nutrient Reduction Strategy Practice/Scenario N management - Maximum Return to Nitrogen Application Rate and 60% of all Corn-Bean and Continuous Corn Acres with Cover Crop Edge-of-Field - 27% of all ag land treated with wetland and 60% of all subsurface drained land with bioreactor Nitrate-N Reduction % (from baseline) Total Equal Annualized Cost Million $/yr 42 756
Treated Acres
Treated Acres ~7600 wetlands
Treated Acres ~7600 wetlands ~120000 bioreactors
What Might it Take to Reach our Goals? Example: Combination Scenarios that Achieves N Goal From Non-Point Sources for Nutrient Reduction Strategy Practice/Scenario N management - Maximum Return to Nitrogen Application Rate and 25% of all Corn-Bean and Continuous Corn Acres with Cover Crop Land Use - 25% of acreage with Extended Rotations Edge-of-Field - 27% of all ag land treated with wetland and 60% of all subsurface drained land with bioreactor Nitrate-N Reduction % (from baseline) Total Equal Annualized Cost Million $/yr 42 542
What are Values of Cover Crops?
DRAINAGE-WETLAND INTEGRATION
Drain Capacity Study in 1980 s investigated drainage in the Des Moines River Basin Drain capacity of many drainage district mains evaluated Example: Calhoun County Avg. drainage coefficient of 38 mains was 0.18 in/day Range in drainage coefficient from 0.05 to 0.44 in/day
How much do Under Designed Systems Impact Yield? 100 90 These estimates are likely on the conservative side. Relative Yield (%) 80 70 Webster Nicollet Okoboji Yield impacts are likely greater. 60 50 0.0 0.2 0.4 0.6 0.8 1.0 Drainage Coefficient (in/day)
DD - 2005
DD - 2008
DD - 2010
DD - 2011
DD - 2014
DD - 2015
Value of Wetlands Water quality benefits Opportunities to integrate with drainage Waterfowl and wildlife benefits Biodiversity benefits in the buffers around wetlands
Wrapup Iowa Nutrient Reduction Strategy calls for a 41% reduction in nitrate-n from nonpoint sources In-field nitrogen management has some potential to reduce nitrate-n loss however other in-field and edge-of-field practices will be needed to reach the goals Level of implementation to reach the goals is very large In future can we look at value of these practices
Contact mhelmers@iastate.edu Twitter: @ISUAgWaterMgmt Website: http://agwatermgmt.ae.iastate.edu/