Agricultural Drainage: How it Works and When it Should be ......Agricultural Drainage: How it Works and When it Should be Considered Gary R. Sands, Dept. of Biosystems & Agricultural

Agricultural Drainage: How it Works and When it Should be Considered

Gary R. Sands, Dept. of Biosystems & Agricultural Engineering, University of Minnesota, St. Paul, MN [email protected]

Agricultural DrainageHow it Works & When it Should be ConsideredAgricultural DrainageHow it Works & When it Should be Considered

Gary R. Sands, Extension EngineerDept. of Biosystems & Agricultural Engineering

OverviewOverview

Resources

How to determine if drainage is neededDrainage benefits

How does drainage work—some technical background

drainage planning & design (next time!)

Important Planning PublicationsImportant Planning Publications

Ontario Ministry of Agriculture, Food and Rural Affairswww.gov.on.ca/omafra

Important Planning PublicationsImportant Planning PublicationsUniversity of Minnesota Extension Service

www.extension.umn.edu

The “Drainage Outlet” Website http://d-outlet.coafes.umn.eduThe “Drainage Outlet” Website http://d-outlet.coafes.umn.edu What is Artificial Drainage?What is Artificial Drainage?

Subsurface Drainage

Surface Drainage



To Drain, or Not To Drain . . . To Drain, or Not To Drain . . .

Many production benefits from drainage

…But many issues surround the practice

The Pro’s and Con’s of DrainageThe Pro’s and Con’s of DrainageADVANTAGES

Reduces surface runoff

Reduces soil compaction

Increase crop yields

Decreases yield variability

Enhances timing of field operations

Can extend growing season

Can provide more crop options for rotation

DISADVANTAGESCan increase losses of some nutrients

May increase localized flooding (overloading of mains)

Can impact wetlands

Can disrupt flow of groundwater

High capital costs

Maintenance costs

Benefits of DrainageBenefits of Drainage Damage Due to Excess Soil WaterDamage Due to Excess Soil Water

Crop response to poor aerationCrop emergence problemsStunted crop growth with wet conditions early & late

Timeliness of field operations affected

Traffic patterns interrupted

Buildup of salts in crop root zone

Soil compaction worsened on wet soilsCompaction effect is long-term!

Excess Soil Water Will:Excess Soil Water Will:

Restrict Root Access to Oxygen

Result in incomplete root respiration

Cause formation of acidic compounds in root cells, which kills root cells.

Reduce plant access to soil nutrients

Reduce plant growth rate, or kill plants.

Excess Soil Water Will:Excess Soil Water Will:

Create Anaerobic conditions in the soil root zone.

Promote formation of chemically reduced compounds, some of which are toxic to plants.

Reduce or stop growth of plant roots, which will reduce crop yield.



Crop Response to DrainageCrop Response to Drainage

Ontario Crop Yields – 1979-1986

Yield (bu/ac) Crop Undrained Drained % IncreaseWinter Wheat Spring Grain Corn Soybeans

44 36 75 30

61 58 101 37

39 61 35 23

Source: Handbook of Drainage PrinciplesOntario Ministry of Agriculture, Food and Rural Affairswww.gov.on.ca/omafra

Delayed Planting & Crop YieldDelayed Planting & Crop Yield

Barley

Corn

Soybeans

Expected No. of Field Workdays on Drained Soil

Expe

cted

% o

f Max

imum

Yie

ld

Duration of waterlogging between germination & emergence, (days)

Perce

nt of

seed

s pro

ducin

g see

dling

s

4 8 2000

100

80

Wheat (winter) Emergence (1982)Wheat (winter) Emergence (1982)

A similar, dramaticcurve exists

for other crops

Understanding the Need for DrainageUnderstanding the Need for Drainage

Rainfall & water balance factorsSeasonality, storm characteristics, crop water use

Soil factorsSurface or subsurface problem?Limiting factors for good internal drainage

Field ObservationsField Observations Understanding the Need for DrainageUnderstanding the Need for Drainage

Crop symptoms?

Soil too wet—for too long? Excess water? Find out why?

Fluctuating high water table, seep, spring, cultivation pan, compaction

Dig a pit – assess by horizon

Follow procedure outlined in “Handbook of Drainage Principles”, Appendix A- 4.



Source: Handbook of Drainage PrinciplesOntario Ministry of Agriculture, Food and

Rural Affairswww.gov.on.ca/omafra High Water Table SoilsHigh Water Table Soils

JAN MAR MAY JUL SEP NOV

0

1

2

3

4

5

6

ROOT DEPTH

Dept

h Be

low

Grou

nd S

urfa

ce

POORLY D

RAINED

SOMEWHAT POORLYDRAINED

SOMEW

HAT

WELL DRAINED

Seasonal Water BalanceSeasonal Water Balance

Sour

ce: H

andb

ook

of D

rain

age

Prin

cipl

esO

ntar

io M

inis

try

of A

gric

ultu

re, F

ood

and

Rur

al A

ffairs

ww

w.g

ov.o

n.ca

/om

afra

How Does Drainage Work?How Does Drainage Work?

Precipitation, P

Evapotranspiration, ET

Runoff, R

Soil WaterStorage, S

watertable

Drainage, D

restrictive layer

Deep Percolation, DP

Precipitation, P

Evapotranspiration, ET

Runoff, R

Deep Percolation, DP

Soil WaterStorage, S watertable

restrictive layer

P = R + ET + DP P = R + ET + DP + D

Precipitation =

A Simple Water BalanceA Simple Water Balance

If it doesn’t rain….it doesn’t drain!

Runoff

ET

Soil Moist

Deep Perc

Runoff

ET

Soil MoistDeep Perc

Drainage



Forms of Soil WaterForms of Soil Water Soil Water Characteristic CurveSoil Water Characteristic Curve

Volumetric Water Content(in/in)

Tens

ion,

(bar

s)

0.25 0.400.30 0.35

Saturation

Plant Available Water

Drainable Water

WP15

FC1/3

Drainable Water & Soil TypeDrainable Water & Soil Type

Volumetric Water Content(in/in)

Tens

ion,

(bar

s)

0.25 0.400.30 0.35

FC

Clay

SandDrainable Water

Drainable Water

Drainable Porosity ValuesDrainable Porosity Values

Example: a 5% drainable porosity means that the watertable drops/rises 100 inches for every 5 inches of water drained.

Soil Texture

FieldCapacity

(% by vol)

Wilting Point(% by vol)

DrainablePorosity

(% by vol)

clays, clay loams, silty clayswell structured loamssandy

30-50 %20-3010-30

15-24 %8-173-10

3-11 %10-1518-35

Volume of Water DrainedVolume of Water Drained

Example: A clay loam soil with a watertable at 6” below the soil surface is drained to a watertable depth of 3.5’. How much water was drained from the soil profile?

Solution: Assuming a Pd of 8%, the volume drained is:vol = 8 × (3.5’ - .5’) ÷ 100 = 0.24’ = 2.88”

Drainage Flow PatternsDrainage Flow Patterns

Drain flows enter tile from all sides (even from below!)

Soil, drain spacing, depth to impermeable layer are factors



Influence of Drain SpacingInfluence of Drain Spacing Influence of Drain DepthInfluence of Drain Depth

Influence of Drain DepthInfluence of Drain Depth

Various spacing/depths achieve a “similar” design water removal rate

standard

shallower & closer

Soil Water Distribution w/DepthSoil Water Distribution w/Depth

Pore Volume(% of soil volume)

Watertable

Hei

ght A

bove

Wat

erta

ble

25 4030 35

Soil Surfacee.g. field capacity = 28%

emptypores

% air% water

water-filledpores

“Under” and “Over” Drainage“Under” and “Over” Drainage

Drainage Depth, (ft.)

Decre

ase i

n Cro

p Yiel

d, (%

)

sandy loam

clay loampeat060

1 5

Soil Type and Depth/SpacingSoil Type and Depth/Spacing

Fine soils: narrower and shallowerLower permeabilities

Coarse soils: wider and deeperGreater permeabilities



SummarySummary

Assess drainage needs carefully

Draw on local experience and drainage professionals

Soil is primary factor in the “physics” of drainage

Be aware of water quality considerations when planning for drainage

Upcoming WorkshopsUpcoming Workshops

Annual Drainage and Water Management Workshops (CCA credits available)

Crookston, Feb 25th – 27thMankato, March 3rd – 6th

Pore Volume(% of soil volume)

Hei

ght A

bove

Wat

erta

ble

25 4030 35

Soil Surface

Volume of Water DrainedVolume of Water Draineddrainedporesemptypores

water-filledpores

initial watertable position

h

final watertable position

120 - 140Sugar Beets

120 - 130Sunflowers

110 - 140Potatoes

110 - 120Corn (Grain)

105 - 115Fababeans

95 - 105Canary Grass Seed

95 - 105Black Beans

92 - 102Canola - late Argentine

90 - 100Wheat

90 - 100Navy Beans

90 - 100Field Peas

90 - 100Coriander

85 - 100Lentils

85 - 100Flax

85 - 95Brown or Oriental Mustard

85 - 88Oats

80 - 90Yellow Mustard

80 - 90Buckwheat

73 - 83Canola - early Polish

60 - 90Barley

Days to MaturityCrop



Climate Normals (Brandon, 1971-2000)Climate Normals (Brandon, 1971-2000)

0

10

20

30

40

50

60

70

80

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rai

nfal

l (m

m)

0

1

2

3

4

5

6

7

8

9

10

Num

ber o

f Day

s

>=5mm

>=10mm

>=25mm

25% of Ag Soils are Artificially Drained25% of Ag Soils are Artificially Drained Extent of Subsurface Drainage (’92)51 million ac of corn-belt

Extent of Subsurface Drainage (’92)51 million ac of corn-belt



Drainage FlowDrainage Flow

Documents

Agricultural Drainage: How it Works and When it Should be ......Agricultural Drainage: How it Works and When it Should be Considered Gary R. Sands, Dept. of Biosystems & Agricultural