Irrigation Efficiency Workshop

Irrigation Requirements and Timing BasicsSalim Bawazir, Ph.D.

Civil Engineering, NMSU

For Teaching Purposes Only

Crop Coefficient

NOTE: Kc could be a function of DOY, Cumulative GDD, Percent Cover etc

ETc Kc ETo

ETcKcETo

= ×

=

For Teaching Purposes Only

Assumptions:

• The climate data are accurate• Actual ET was measured correctly• Crop was not under stress• Farming practices and crop variety have not

changed• Calculations and Units are correct!!• Climates are similar

For Teaching Purposes Only

ASCE Standardized Reference ET Equation

Penman Reference ET Equation

( ) 26.43(1 0.53 )( )oo z zE Rn G u e eγλ

γ γ ∆

= − + + − ∆ + ∆ +

For Teaching Purposes Only

0

2

4

6

8

10

12Ev

apotr

ansp

iratio

n, mm

/day

100 125 150 175 200 225 250 275 300Day of Year

Lysimeter ASCE P-M

Kimberly, Idaho 1969

Full cover alfalfa - Data from Dr. J.L. Wright

From Dr. Rick Allen, IdahoFor Teaching Purposes Only

Standardized ReferenceEvapotranspiration Equation (ETsz)

“reference evapotranspiration is defined as the ET rate from a uniform surface of dense, actively growing vegetation having specified height and surface resistance, not short of soil water, and representing an expanse of at least 100 m of the same or similar vegetation.”

For Teaching Purposes Only

Required data

The calculation of ETsz requires measurements or estimates for:

• air temperature• humidity• solar radiation• and wind speed.

For Teaching Purposes Only

For Teaching Purposes Only

Kc Vs. DOY (PECAN)

1 29 57 85 113 141 169 197 225 253 281 309 337 365Day of Year 2003

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Cro

p C

oeffi

cien

t, Kc

FAO56 Penman Penman-Sammis

For Teaching Purposes Only

Kc Vs. Percent Cover

Calculated Pecan Crop Coefficient

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

1 29 57 85 113 141 169 197 225 253 281 309 337 365Day of Year, 2003

Kc

ETszETo_HS

For Teaching Purposes Only

Net Radiation

Short Wave Long Wave

Rs Rs(α) RL_d RL_up

For Teaching Purposes Only

For Teaching Purposes Only

What if Kc and actual ET are not Available ? Use Rn

Pecan ET- 2003

0

5

10

15

20

25

1 29 57 85 113 141 169 197 225 253 281 309 337 365Day of Year, 2003

ET/R

n (M

J/m

²)

ET MeasuredRn

For Teaching Purposes Only

For Teaching Purposes Only

For Teaching Purposes Only

For Teaching Purposes Only

Irrigation 68 inchesRain = 9 inchesET = 56 inches

For Teaching Purposes Only

Daily Measured ET of Alfalfa (Willie’s Farm) including the Cutting Dates

ET of alfalfa = 4.6 ft (1403 mm)

Precipitation = 11 in or 0.92 ft (277 mm)

Irrigation Applied = 5.67 ft (1729 mm)

N= 271 days of data collection

Recharge to Groundwater: 1.0 - 1.5 ft

For Teaching Purposes Only

Evapotranspiration (ET) Measurements

Eddy Covariance Flux and Microclimate MeasurementsIn the Central Mesilla Valley, New Mexico

For Teaching Purposes Only

Thank you

E-mail: abawazir@nmsu.edu

For Teaching Purposes Only