Drainage Management for Water Quality and Crop Production Benefits Don Pitts Agricultural Engineer NRCS USDA Champaign, IL
Midwest Subsurface Drained Farmland Midwest total > 50 million acres
Benefits of Drainage • Many of the most agriculturally productive soils in Illinois require subsurface drainage for economic crop production • Subsurface drainage allows for improved soil aeration and increased crop production • Subsurface drainage allows for field access with equipment cultivation, planting, harvesting, etc.
Distribution of Subsurface Tile Drainage in Illinois 3-4 million ha (6-10 million acres) drained with subsurface tile in Illinois This comprises some of the most productive agricultural land in the US. Graphic based on soils that would benefit from drainage
MCL Unpublished Data: K. Smiciklas, ISU (Lake Bloomington Project) Nitrate Concentrations from Tile Drains(McLean Co, IL. 1997-1998) Corn following Soybeans * new tile system
Distribution of tile-drained soils and nitrate in surface water in Illinois
Problem Statement • Tile drainage is needed for economical crop production • Tile drainage water is a primary source of nitrate to surface water
Possible Solutions • Reduce the amount of N applied (source reduction) • follow U of I nitrogen fertilizer guidelines • Practice drainage management (affect the transport process) • only release tile water when it is necessary to release it
Why is drainage needed? • Due to high water tables, many soils in Illinois need drainage for economical crop production: • to insure trafficable field conditions • to minimize crop stress from excess water
Soil Surface 2 ft 4 ft Water Table Tile Tile In humid regions subsurface drainage is needed to lower the water table Role of Drainage
When is drainage not needed? • During the fallow season • During growing season • in dry periods • after planting when the plant root system is small
What is Drainage Management? • Allows for changing the elevation of drainage outlet • Raising the water table can reduce the amount of nitrate discharged from the field through the tile lines • Raising the water table after planting can keep water and nutrients available for plant use during the growing season
Fallow Season Drainage Management Soil Surface 0.5 ft Water Table with Drainage Management 4 ft Tile Tile Water table is raised above tile lines
Tile Flow and Surface Runoff vs Tile Spacing Relationship Typically High in NO3 Relatively Lower in NO3 DRAINMOD Simulations: Gilford soil, tile depth 1 m .
Tile Flow vs Runoff at Different Water Table Depths(with drainage management from Nov - Mar) 36% Reduction DRAINMOD Simulation: Soil - Drummer, 30 m drain spacing, 1 m drain depth, Urbana rainfall and temperature data, and controlled-drainage (Nov 1st-Mar 15st).
Tile NO3-N Discharge(DRAINMOD- N Simulation) Soybean-Corn Rotation, Tile Spacing= 100 ft, Soil=Drummer, Ks = 1 inch/hr, Climate Data=Urbana NM = No Drainage Management, DM = Drainage Management (period of raised water table Oct 15 to Mar 15)
Soil Surface 1 ft Water Table with Drainage Management 4 ft Tile Tile Water table is lowered as root system develops Production Season Drainage Management(when plants are young)
Soil Surface 2 ft Water Table with Drainage Management Tile Tile Water table lowered as root system develops Production Season Drainage Management(when plants are older) 4 ft
~ 1.5 inches Potential Water Available from Drainage Management Source: Based on DRAINMOD Simulations
Raised Water Table Crop Water Uptake Drain down Lower Water Table as Roots Develop Depth below surface After Planting Allow Water Table to Rise Fallow Season Fallow Season Harvest Dec 31 Planting Jan 1 Time line Water Table Level with Drainage Management
Raised Water Table Ditch Drain Water Riser Boards (Adjustable) Drainage Management Control Structure is Placed in Tile Line Water Level Control Structure Soil Surface The water level control device is installed in the tile drain near the outlet and at various locations within the field depending on topography Solid Pipe
Field Boundary laterals laterals main main Water level control structure Drainage Management(Parallel System and Flat Topography)
602 Zone of influence > 20 ac 600 Water Level Control Device Solid Pipe Drainage Management System (gentle sloping topography) Field Boundary
Site Conditions for the Practice of Drainage Management * • Nitrate is a water quality concern in the watershed • Flat topography (slopes < 0.3%) • Intensive subsurface drainage system (pattern system) • No (minimal) impact to neighbors • Field size should be greater than 20 acres * Illinois NRCS Drainage Management Demonstration Project
Structures Installed Structures Planned Structures Proposed Drainage Management Pilot Status Report (March 2000)
Water Level Control Device Cost => $200 to $1000 depending on size plus installation Simple to operate
Excavate Drain Line Installation of Water Level Control Device Water Level Control Box
Anti-seep Collar Installation of Water Level Control Device 20 ft of Solid Pipe
Key Anti- Seep Collar Installation of Water Level Control Device
Hand back fill around Box Installation of Water Level Control Device
Installation Complete Installation of Water Level Control Device
Production Season Drainage Management Considerations • Principle 1. Only release water sufficient to allow for the soil to dry for field access with equipment and to keep the water table out of the root zone. • Any water released in excess of these two requirement is water and nutrients lost from production.
Production Season Drainage Management Considerations • Principle 2. Know the depth of the effective root zone. • If the water table is allowed to rise into the root zone for a prolonged (this depends on temperature) period, oxygen will be depleted and plant stress will soon follow. • This is the greatest risk in practicing drainage management.
Soil Redox Potential (Days after Initiation of a Raised Water Table) Pitts, et al. 1991
Soil Temperature Effects on Oxygen Depletion Arrhenius Rule (Gilmore, 1984)
Potential Benefits of Drainage Management • Reduced Nitrate to Surface Water • by inhibiting nitrification • by reducing the rate of mineralization • by increasing denitrification • by altering the hydrology • Increased Crop Production • because more water is available for ET • because more N available for crop uptake
Subsurface tile line Flow monitor Control Structure Weather Station Monitoring well 40-acre experimental field 40-acre control field Monitoring Equipment at a Demonstration Site
Golden Rule of Drainage • Only release the amount water necessary to insure trafficable conditions for field operations and to provide an aerated crop root zone • any drainage in excess of this rule likely carries away nitrate and water that is no longer available for crop uptake