1. TAWC PET Website Review
2. PET Irrigation Scheduling
3. Cotton Response to Small
Amounts of Water
Bob Glodt
Agri-Search, Inc.
Plainview, Texas
TAWC PET
Website Review
Bob Glodt
Agri-Search, Inc.
www.tawcsolutions.org
Log In, Create a New Account,
Request a New Password
TAWC Home Page
Weather Tab
“About” Contact Tab
“About”
Links
Tab
About “Usage Instructions” Tab
TAWC Home Page
Creating a New Production Site
Manage Water Balance Crops
Creating A New Water Balance
Track For “Water College” Field
New Production Site Created
Water Balance Fields Created
“Water College Field 1” Added
Water Balance Tables
Data That You Control – Rainfall
Rainfall amounts are imported from
the weather station you selected when
the water balance track was created.
 Rainfall amounts can be changed to
more accurately reflect the actual
amount of rain that fell on any
particular farm.
 The effectiveness of the rain can also
be adjusted from 0 to 100%.

Changing Rainfall Data
Changing Effective
Rainfall Data
Data That You Control – Irrigation
Irrigation amounts are entered by the
grower on the day the irrigation was made.
 The effectiveness of the irrigation can be
adjusted from 0 to 100%.

TAWC Moisture Balance Data
Moisture balance data is intended to
represent the amount of moisture in the
soil profile.
 I do not use the water balance
information provided on the website
when making irrigation management
decisions.
 This is one area that needs refinement
and additional research to accurately
calculate water balance.

QUESTIONS?
PET Irrigation
Scheduling
Days After Planting
maturity
first open boll
first bloom
first
square
emergence
Inches Per Day
Cotton Water Demand
at 100% of PET
Calculating Your Ability to
Irrigate at a Specific % of PET
100% PET =
7 days x 0.3” per day
= 2.10” per week
1.25” Per Week =
1.25” divided by 2.10”
= 59.5% of PET
Days After Planting
maturity
first open boll
first bloom
first
square
Maintain Adequate
Moisture in Root
Zone
emergence
Inches Per Day
PRE-FLOWER IRRIGATION
STRATEGY
FLOWER TO 1ST OPEN BOLL
IRRIGATION STRATEGY
Days After Planting
maturity
first open boll
first bloom
first
square
emergence
Inches Per Day
FILL
PROFILE
IRRIGATE AT
% OF PET
APPLY LOGIC
Prior to canopy closure the
majority of water loss is from
evaporation.
After canopy closure the majority
of water loss is through
transpiration.
Fundamental Principles of
Irrigation Management
Your irrigation system must be
efficient.
 More water less often is better than
less water more often.
 Irrigate at a consistent percentage of
PET during the peak water demand
period.

Irrigating at 60% of PET
DATE
GROWTH
STAGE
100%
PET
RAIN
IRRIG.
60%
DEFICIT
7-26-15
1ST Bloom
0.12
0
0
0.07
7-27-15
0.13
0
0
0.15
7-28-15
0.14
0
0
0.23
7-29-15
0.12
0
0
0.30
7-30-15
0.12
0
0
0.37
7-31-15
0.13
.55
0
-0.10
8-01-15
0.10
0
0
0
8-02-15
0.14
0
0
0.08
0.14
0
0
0.16
8-04-14
0.16
0
0
0.26
8-05-15
0.17
0
0
0.36
8-06-15
0.20
0
0
0.48
8-03-15
E. Bloom
Irrigating at 60% of PET
100%
PET
RAIN
IRRIG.
60%
DEFICIT
8-07-15
0.20
0
0
0.60
8-08-15
0.19
0
0
0.71
0.14
0
0
0.79
8-10-15
0.09
0
0
0.84
8-11-15
0.21
0
0
0.50
8-12-15
0.20
0
0
0.62
8-13-15
0.22
0
0
0.75
8-14-15
0.15
0
0
0.84
8-15-15
0.21
0
0
0.97
8-16-14
0.22
0
0
1.10
8-17-15
0.22
0
0
1.23
8-18-15
0.22
0
1.25
0.11
DATE
8-09-15
GROWTH
STAGE
M. Bloom
QUESTIONS?
Cotton Yield Response
To Small Amounts of
Water
2015 Cotton WUE Trial –
Irrigation Plus Rainfall (inches)
Growth Stage Rainfed
Pre-Plant
Emergence to
Square.
Square to 1st
Bloom
60% ET to 1st
Open Boll (R)
Total Pre PET
Rainfall
60% ET to 1st
Open Boll (I)
30% PET
60% PET 90% PET
6.6
6.6
6.6
6.6
2.3
2.3
2.3
2.3
8.7
8.7
8.7
8.7
1.24
1.24
1.24
1.24
18.84
18.84
18.84
18.84
0
1.71
3.41
5.12
2015 Cotton WUE Trial
Yield Ranges For 12 Varieties
Yield
Range
Rainfed
30%
PET
60%
PET
90%
PET
Low
529
909
1335
1205
High
862
1140
1214
1543
Diff.
333
231
121
338
Avg.
660
1015
1280
1423
+ Irr.
0
1.71
3.41
5.12
Yld/in.
N/A
207.6
155
83.6
2015 Cotton WUE Trial
Loan Value Per Acre For 12 Varieties
Yield
Rainfed
Range
30%
PET
60%
PET
90%
PET
Low
302.43
514.35
687.91
696.05
High
449.21
629.57
780.15
922.60
Diff.
146.78
115.22
92.24
226.55
Avg.
380.47
573.20
738.69
792.88
+ Irr.
0
1.71
3.41
5.12
$/Ac/in.
N/A
112.71
96.78
31.69
QUESTIONS?