drainage challenges drainage design for crop

Drainage Design for Crop Production and Environmental

Benefits

Matt Helmers Professor and Director of the Iowa

Nutrient Research Center

Drainage Challenges• Agricultural drainage in Midwest is

contributor to elevated levels of nitrate that contribute “hypoxia”

• Nitrate levels from most drains exceed drinking water standards

• In many areas, outlet costs are high and may limit effectiveness of field drainage investment

Goals of Drainage

• Primary goals of agricultural drainage in humid areas are to:– provide for improved site trafficability for

timely planting and harvesting, and– lower the water content in the root zone to

provide adequate aeration following excessive rainfall.

Forms of Soil Water

Forms of Water in Soil• Gravitational (0.5” per foot of soil)

– Removed with drain lines• Plant Available (2.25” per foot of soil)

– Water held in pores that plants can use but is held against gravity (Field capacity-Wilting Point)

• Plant Unavailable – Held so tight that plants can’t extract

Drainage Coefficient and Drainage Intensity

• Drainage coefficient –how much water can exit the system in a unit of time – sizing of pipe

• Drainage intensity – how much water can get to the drainage system in a unit of time -spacing of the drainage system

• What controls outflow from the system? –Depends on system design

Drainage SystemMain

Laterals

Drainage IntensityMain

LateralsHow quickly we can get water to the drain

Drainage CoefficientMain

Laterals

How quickly drains can take it away

Required Drainage CapacityDrained Area = A (acres)

Flowrate (Q) = DC x ADC = Drainage Coefficient

Drainage Coefficient –Amount of water that can be removed in a 24 hour period

Recommended Drainage Coefficients (NRCS Field Handbook)

Soil Type

Inches to be removed in 24 hours

Field crops Truck cropsMineral 3/8 to 1/2 1/2 to 3/4

Organic 1/2 to 3/4 3/4 to 1.5

Drain Depth and Spacing• Spacing determines

drainage intensity• Important for uniformity

of drainage• Use regional guides,

computations for soil conditions, experience

• Need to make sure drain is placed above the impermeable layer

Drain System Cross-Section

dc)hh(2d4KL

2ee2

L = spacing between laterals (ft)Ke = hydraulic conductivity (ft/day)h = water table height above laterals (ft)dc = drainage rate (ft/day)de = equivalent depth of impermeable layer below pipe drain center (ft)

Hooghoudt Equation

Steady-StateDrainage Design

Example• 80 acres to be drained at 0.375 in/day

drainage coefficient with grade on the main of 0.25% – 12 inch pipe

• Poorly drained soil – Hydraulic Conductivity = 0.7 in/hr– Drainage Intensity = 0.375 in/day with 65 ft. drain

spacing at 4 ft depth– Drainage Intensity = 0.86 in/day with 40 ft.

drainage spacing at 4 ft depth• http://www.igrowdrainage.org

Impact of Drainage Coefficient

Drainage Coefficient (in/day)

0.0 0.2 0.4 0.6 0.8 1.0

Rel

ativ

e Yi

eld

(%)

50

60

70

80

90

100

Poorly drainedSomewhat poorly drainedVery poorly drained

How Does Drainage Coefficient Potentially Impact Yield – Modeled Results

These estimates are likely on the conservative side.

Yield impacts are likely greater.

3/8” Drainage Coefficient

Drain Spacing

Crawfordsville, IADrainage Spacing Research

45

75

60

No

30

NDrain Spacing

• Spacing may control drainage coefficient

• Important for uniformity of drainage

• Use regional guides, computations for soil conditions, experience

% Clay in Subsoil

Garwin Poor 27-35 60-80 80-100

Taintor Poor 35-42 60-80 80-100

Haig Poor 42-48 40-50 50-60

Edina Poor 48-56 20-30 40-50

Taintor and Kalona silty clay loams• Poorly drained - loess soil• Water table 1.0 to 2.0 ft depth• Permeability (0-40 in.) 0.2-0.6 in/hr• Clay content:

– 0-18 in. 30-36%– 18-40 in. 35-44%

• Iowa Drainage Guide recommendation– 3’ depth – 60-80’ spacing– 4’ depth – 80-100’ spacing

Installation – SE Tile Study

• 500 ft length• 30, 45, 60, 75 ft. spacing• 4 inch perforated laterals• 4 ft depth• 0.1- 0.2 % grade• All tile trenched in summer 1999

0

1

2

3

4

5

6

3/1/2009 4/1/2009 5/2/2009 6/2/2009 7/3/2009 8/3/2009 9/3/2009

Gro

undw

ater

Dep

th (

ft)

Check Well 30 Foot 45 Foot 60 Foot 75 Foot

Water Table Depths - 2009

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

6/6/2009 6/8/2009 6/10/2009 6/12/2009 6/14/2009 6/16/2009 6/18/2009G

roun

dwat

er D

epth

(ft

)Check Well 30 Foot 45 Foot 60 Foot 75 Foot

0.6” rain

Water Tables - June 2009

1.8” rain

0

5

10

15

20

25

30

200 foot 75 foot 60 foot 45 foot 30 foot

Occ

uran

ce D

ays

6 in 12 in 18 in 24 in

2009 – Water Table Depth Frequency

Tile Spacing

2000 12.472001 15.802002 12.542003 13.372004 9.832005 8.382006 7.462007 18.492008 16.962009 16.87

21 yr Avg 11.90

SE Farm April – June Rainfall

SERF Tile Spacing Study YieldsTile

Spacing2001Corn

2003 Corn

2005 Corn

2007 Corn

2009 Corn

Ck – 200’ 170 172 179 170 19475' 179 186 177 192 20660' 177 188 175 189 20945' 178 188 178 192 20630' 176 187 180 192 207

SERF Tile Spacing Soybean YieldsTile

Spacing2000

Beans2002 Beans

2004 Beans

2006 Beans

2008Beans

Ck – 200’ 47.4 58.1 65.6 51.4 62.175' 46.5 56.7 66.3 50.5 64.260' 45.7 55.3 67.1 50.8 62.045' 45.9 56.6 69.0 50.7 65.430' 47.1 55.9 65.4 51.1 63.5

Drainage Design and Management to Consider Economics and Environment

Drainage water management

Constructed Wetland

Weir Boxes

2.5 ft. tile depth with 40 ft. spacing

4 ft. tile depth with 60 ft. spacing – with Control boxes

4 ft. tile depth with 60 ft. spacing

Annual flow-weighted nitrate-N concentrations for three drainage systemsPoints with the same letter (or no letters) for the same year are not significantly different at the P=0.05 level.

Annual drainage volume and nitrate-N load for three

drainage systemsBars with the same letter (or no letters) for the same year are not significantly different at the

P=0.05 level.

Annual corn yield from three drainage systems and undrained system Bars with the same letter (or no letters) for the same year are not significantly different at the P=0.05 level.

Department of Agricultural and Biosystems Engineering

Drainage Challenges

• Agricultural drainage in Midwest is being targeted as contributor to “hypoxia”

• Nitrate levels from most drains exceed drinking water standards

• In many areas, outlet costs are high and may limit effectiveness of field drainage investment


Drainage Design• Production benefits of drainage• Environmental impacts of drainage

through increased nitrate-nitrogen losses• Can drainage design maximize production

and net return while minimizing environmental impacts?• There are opportunities


Simulations of Response to Subsurface Drainage

• Can’t afford field investigations on many soils, over many years, and for many drainage spacings.• So, use a model that can represent major

components of the systems (water flow and crop response to water stress – drought and excess water stress)

• DRAINMOD

Effects of Drain Spacing on Drainage and Surface Runoff – North-Central Iowa

Drain spacing (ft)

0 50 100 150 200 250 300 350

Surf

ace

runo

ff o

r sub

surf

ace

drai

nage

(in)

0

2

4

6

8

10

12CANI_NC RunoffNICO_NC RunoffOKOB_NC RunoffCANI_NC DrainageNICO_NC DrainageOKOB_NC Drainage

Effects of Drain Spacing on Relative Corn Yield –North-Central Iowa

Drain spacing (ft)0 50 100 150 200 250 300 350

Rel

ativ

e yi

eld

(%)

20

40

60

80

100

CANI_NC NICO_NC OKOB_NC

Range of drain spacingTo maximize relative yield for Canisteo

Drain spacing (ft.)0 20 40 60 80 100 120 140 160

Rel

ativ

e yi

eld

(%)

40

50

60

70

80

90

100

Range in Relative Yield for Canisteo – 40 yr results

90th Percentile75th Percentile

25th Percentile

MeanMedian

10th Percentile

Drain spacing (ft)0 50 100 150 200 250 300 350

Net

ann

ual r

etur

n fo

r dra

inag

e sy

stem

($/a

cre)

-300

-200

-100

0

100

200

300

CANI_NCNICO_NCOKOB_NC

Effects of Drain Spacing on Net Annual Return –North-Central Iowa

Range of drain spacingTo maximize net return for Canisteo

Range of drain spacing to maximize crop production and net annual return

Region Soil seriesRange of drain spacing (ft.) to

maximizeCrop production Net annual return

North East CLYDE 40-60 60-80CLYDE-FLOYD

COMPLEX 40-60 65-85

TRIPOLI 40-60 45-65North Central NICOLLET 55-75 115-135

CANISTEO 40-60 80-100OKOBOJI 25-45 70-90

Central NICOLLET 55-75 115-135CANISTEO 45-65 80-100

HARPS 30-50 55-75South East TAINTOR 45-65 45-65

HAIG 40-60 60-80CLARINDA 25-45 45-65


Drainage Guide Recommendations

Soil Natural soildrainage

Spacing at 36 inch depth

Spacing at 48 inch depth

Nicollet Moderately well to somewhat poor

70-80 90-100

Canisteo Poor 70-80 90-100Tama Well 80-90 100-110Dinsdale Well to moderately

well- -

Clyde Poor to very poor 60-80 70-100Floyd Somewhat poor 60-90 70-100Kenyon Moderately well to

well60-80 80-90


Overall Summary for Drain Spacing• Subsurface drainage has led to increased productivity

in many areas• Not all soils need the same drain spacing• Drain spacing may be different depending on design

objectives• Overall average long-term yield will vary as a function

of drain spacing• Drainage design should consider costs and potential

return• Drainage design in the future may need to consider

both economic and environmental aspects

Wrapup• Drainage design needs to consider

drainage coefficient and drainage intensity• Drainage benefits crop yield in situations

with high water tables• Drainage design should consider

economics as well as environmental impacts

Contact

• [email protected]• Twitter: @ISUAgWaterMgmt• Website: http://agwatermgmt.ae.iastate.edu/

drainage challenges drainage design for crop

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