Drainage Management for Water Quality and Crop Production Benefits

Don Pitts

Agricultural Engineer

NRCS USDA

Champaign, IL

Midwest Subsurface Drained Farmland

State Acres Percent ofCropland

U.S.Rank

Illinois 9.8 million 35 1

Indiana 8.1 50 2

Iowa 7.8 25 3

Ohio 7.4 50 4

Minnesota 6.4 20 7

Michigan 5.5 30 11

Missouri 4.2 25 113

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 millionacres) drained with subsurface tile inIllinois

This comprises some of the most productive agricultural land in theUS.

Graphic based on soils that would benefit from drainage

Nitrate Concentrations from Tile Drains (McLean Co, IL. 1997-1998)

0

5

10

15

20

25

30

35

40

45

16-Nov 5-Jan 24-Feb 15-Apr 4-Jun 24-Jul

NO

3-N

mg/

l

O # N125 # N Spring140# N Sidedress175 # N Fall AA175 # N N-Serve

Unpublished Data: K. Smiciklas, ISU (Lake Bloomington Project)

MCL

Corn followingSoybeans

* 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

Role of Drainage

4 ft

Soil Surface

Tile

Water Table Tile

In humid regions subsurface drainage is needed to lower the water table

2 ft

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

4 ft

Soil Surface

Tile

Water Table with Drainage Management

Tile

Water table is raised above tile lines

0.5 ft

Tile Flow and Surface Runoff vs Tile Spacing Relationship

0

10

20

30

40

50

0 20 40 60 80 100 120 140

Tile Spacing (m)

Fie

ld W

ater

Los

s (c

m/y

r)

tile flowrunoff

DRAINMOD Simulations: Gilford soil, tile depth 1 m .

Typically Highin NO3

RelativelyLower in NO3

Tile Flow vs Runoff at Different Water Table Depths

(with drainage management from Nov - Mar)

0

10

20

30

40

1 meter M@ 60 cm M@ 30 cm M@ 15 cm

Drainage Treatment

(cm

)

Tile WaterRun off

DRAINMOD Simulation: Soil - Drummer, 30 m drain spacing, 1 m drain depth, Urbanarainfall and temperature data, and controlled-drainage (Nov 1st-Mar 15st).

36% Reduction

Tile NO3-N Discharge(DRAINMOD- N Simulation)

0

5

10

15

20

25

(lb/

ac/y

r)

200 lb N-(NM) 200 lb N-(DM) 140 lb N-(NM) 140 lb N-(DM)

Soybean-Corn Rotation, Tile Spacing= 100 ft, Soil=Drummer, Ks = 1 inch/hr, Climate Data=UrbanaNM = No Drainage Management, DM = Drainage Management (period of raised water table Oct 15 to Mar 15)

Production Season Drainage Management(when plants are young)

Soil Surface

Tile

Water Table with Drainage Management

Tile

Water table is lowered as root system develops

4 ft

1 ft

Production Season Drainage Management(when plants are older)

4 ft

Soil Surface

Tile

Water Table with Drainage Management

Tile

Water table lowered as root system develops

2 ft

Potential Water Available from Drainage Management

0

0.5

1

1.5

2

2.5

3

0 12 24 36 48 60

Depth to Water Table (inches) .

Dra

ined

Vol

um

e (i

nch

es)

.

Sable

Source: Based on DRAINMOD Simulations

~ 1.5 inches

Water Table Level with Drainage Management

Jan 1 Dec 31

Drain downRaised Water Table

After Planting AllowWater Table to Rise

Crop WaterUptake

Fallow Season

Fallow Season

Planting Harvest

Lower WaterTable as RootsDevelop

Dep

th b

elow

su

rfac

e

Time line

Drainage Management Control Structure is Placed in Tile Line

The water level control device is installed in the tile drain near the outlet and at various locations within the field depending on topography

Ditc

h

Raised Water Table

Riser Boards (Adjustable)

Drain Water

Solid Pipe

Water Level Control Structure Soil Surface

Drainage Management(Parallel System and Flat Topography)

Field Boundary

main main

late

rals

late

rals

Water level control structure

Drainage Management System

(gentle sloping topography) Field Boundary

602602

600

600

Water Level Control Device

Zone of influence > 20 ac

Solid Pipe

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 (March2000)

Water Level Control Device

Cost => $200 to $1000depending on sizeplus installation

Simple to operate

Installation of Water Level Control Device

Water LevelControl Box

Excavate Drain Line

Installation of Water Level Control Device

20 ft of SolidPipe

Anti-seepCollar

Installation of Water Level Control Device

Key Anti-Seep Collar

Installation of Water Level Control Device

Hand back fillaround Box

Installation of Water Level Control Device

Installation Complete

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)

-150

-100

-50

0

50

100

150

0 1 2 3 4 5 6 7 8 9

Days after Initiation of Raised Water Table

mV

6-inch12-inch

Pitts, et al. 1991

Soil Temperature Effects on Oxygen Depletion

0

0.2

0.4

0.6

0 5 10 15 20 25 30

Temperature Co

Rel

ativ

e R

eact

ion

Rat

es

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 40-acre control fieldcontrol field40-acre 40-acre control fieldcontrol field

40-acre 40-acre experimental experimental fieldfield

40-acre 40-acre experimental experimental fieldfield

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