Presented at 15th Annual Crop Production Clinic

March 6, 2014; Goodwell, OK

Saleh Taghvaeian

(405) 744-8395 Saleh.taghvaeian@okstate.edu

Presentation Outline

i. Introduction

ii. Main irrigation scheduling methods

1) Evaporometers

2) Mesonet

3) Soil moisture

4) Canopy temperature

iii. Question

Introduction

• Irrigation scheduling is the science (and art) of

determining when and how much water to apply to

maximize water use efficiency and crop production.

• Why irrigation scheduling?

1) Evaporometers

• Measure evaporation of water from a container

• Evaporated water is directly related to crop water use

i. Easy pan

ii. Atmometer

1-i) Easy pan

• Can be home-made with cheap available material

• It accounts for irrigation (sprinkler) and rainfall events

1-ii) Atmometer

• Main Components:

• Green fabric

• Porous ceramic cup

• Water reservoir

• Suction tube

• The green fabric simulates

crop canopy

• Refill with distilled water

• A widely used model: ETgage

http://www.etgage.com/

1-ii) Atmometer

2) Mesonet

• Lots of useful information

• Several weather variables: past and future

2) Mesonet

3) Soil moisture

• Soil moisture limits

3) Soil moisture

Solid particles

Voids

3) Soil moisture

Solid particles

All voids are filled with

water: Saturation

3) Soil moisture

Solid particles

Gravitational water is

drained: Field Capacity

3) Soil moisture

Solid particles

Additional water is extracted

by crops, stress starts: MAD

3) Soil moisture

Solid particles

No more water can be

extracted by crops: PWP

3) Soil moisture

Solid particles

Field Capacity

Maximum Allowable Depletion

Permanent Wilting Point

3) Soil moisture

Clay loam

Corn

FC = 33%

MAD = 25%

PWP = 18%

Saturation = 42%

Estimating irrigation depth:

• FC – MAD = 8%

• Root depth = 3 ft

• Irrigation depth:

0.08 × 3 = 0.24 ft

= 2.9 inches

A

C

C

U

R

A

C

Y

7%

3) Soil moisture

Soil moisture sensors

• Tensiometers

• Electrical resistance

• Heat dissipation

• EM-based:

Capacitance

Travel Time

3) Soil moisture: Tensiometers

3) Soil moisture: Tensiometers

• Have limited range (perform better near FC)

• Work better in heavy soil

• Have slow response time

• Require maintenance Lauren Settles,

Henderson County extension intern, Kentucky

3) Soil moisture: Electrical Resistance

• Also known as gypsum blocks

• The drier the soil, the larger the R

• Can be connected to a data-logger or a hand-held device

• Have limited range (perform better near FC)

3) Soil moisture: Heat Dissipation

• Porous ceramic body

• Heating element

• Thermocouple

• Have a larger range

• Pores may clog

• Affordable

3) Soil moisture: Capacitance

• Send an EM field into the soil

• Soil becomes the dielectric of a capacitor in an oscillating

electric field

• The oscillation frequency decreases as water increases

• But it is also sensitive to temperature, clay content,

salinity, and bound water

• Non-uniform EM field: attracted to more conductive

parts of the soil

3) Soil moisture: Capacitance

3) Soil moisture: Travel Time

• Measure the time it takes a pulse to travel along a rod

• The travel time increases as water increases

• Significantly less sensitive to salinity and temperature

4) Canopy temperature

• Water transpiration requires energy

• The higher the water use rate, the cooler the canopy

4) Canopy temperature

• Hand-held infra-red thermometers

• Less than $150

4) Canopy temperature

• Comparison to a reference

temperature

-15

-10

-5

0

5

10

210 220 230 240 250 260

Ca

no

py T

em

p -

Op

tim

um

Pla

nt

Te

mp

(F

)

Day of Year (2010)

Full Irrigation Treatment

-15

-10

-5

0

5

10

210 220 230 240 250 260

Can

op

y T

em

p -

Op

tim

um

Pla

nt

Tem

p (

F)

Day of Year (2010)

Deficit Irrigation Treatment

4) Canopy temperature

• Comparison to a constant temperature

• Optimum plant temperature for corn < 82 F

4) Canopy temperature

• Comparison to the temperature of a non-stressed plot

• DANS: Degrees Above Non-Stress

4) Canopy temperature

• Comparison to the temperature of a non-stressed plot

• DANS: Degrees Above Non-Stress

4) Canopy temperature: 77 – 113 ˚F

07/1

9/1

2

08

/09

/12

77 77

77 77

113 113

113 113

07

/26

/12

0

9/0

5/1

2