By: Dr. Gaylon S. Campbell Every irrigator wishes for tools that answer the fundamental questions: when do I turn the water on and when do I turn the water off? The challenge is figuring out the right ones and implementing them effectively. New sensor technology and cloud computing offer new opportunities to growers, but it is often unclear how to put these into practice. In this 30-minute webinar, Dr. Gaylon Campbell will cover the different methods for irrigation water management and the pros and cons of each. Best practices for soil moisture monitoring and costs of improper irrigation scheduling will also be discussed. Learn: • Why we schedule irrigation • Different methods used by growers to decide when to irrigate • Steps for scheduling irrigation using soil moisture • Results from good management and the consequences of mistakes

2. HOW TO IMPROVE
IRRIGATION SCHEDULING
USING SOIL MOISTURE
GAYLON S. CAMPBELL, PH.D.
METER GROUP, INC. USA
PULLMAN, WA, USA

3. WHY MANAGE IRRIGATION?
• Produce healthy crops while minimizing costs
and environmental impact
• Control assimilate partitioning and increase
value of harvested products
• Other custom applications (frost control,
nutrient management, waste disposal, etc.)

4. CORRECT IRRIGATION
REQUIRES THE ANSWER TO
ONLY TWO QUESTIONS:
• When do I turn the water on?
• When do I turn the water off?

5. OPTIONS FOR DECIDING WHEN
TO TURN THE WATER ON
• Clock or calendar
• Ask the soil
• Ask the plant
• Ask the atmosphere

6. IRRIGATION SCHEDULING BY
CLOCK OR CALENDAR
Method:
• Apply water on a fixed
schedule
• Simplest of all methods
• Match average supply with
average demand
But:
• Wastes water and nutrients
when demand is low
• Stresses crops when demand
is high

7. IRRIGATION SCHEDULING USING
SOIL MOISTURE MEASUREMENT
Method:
• Install sensors
• Determine full and refill points
• Monitor
Shows water applications
and extraction
Can show drainage
But:
• Soils and crops are variable
• Can’t cover the field with
sensors
• Doesn’t measure the stress
level of plants

8. IRRIGATION SCHEDULING
BASED ON PLANT
MEASUREMENT
Method:
• Measure canopy temp.,
stomatal cond., stem diam.,
fruit diam, water potential, etc.
• Irrigate when the plant says it
needs it
Essential for deficit and
controlled stress irrigation
But:
Water stress from:
• Too little water
• Too much water
• Disease
• High evap. demand
Irrigation can only fix too little
water

9. IRRIGATION SCHEDULING
USING ET (ATMOSPHERE)
• Method:
• Make a water budget
• Measure weather
• Estimate ET
• Irrigate to replenish ET
• Corrects for demand
• Relatively easy and
inexpensive
But:
• How much water was actually
applied?
• How much was actually used?
• Did water drain out the
bottom?

10. WHICH METHOD IS BEST?
• Depends on needs and resources
• Go beyond calendar for modern irrigated agriculture
• Soil moisture monitoring gives best understanding
and control
• ET can give insight into varying demands and can be
effectively used with soil measurements
• Plant measurements essential for controlled
stress irrigation

11. “Since the soil is the primary recipient of
the irrigation water, it seems reasonable that
the answers to these two questions [when
to turn water on and when to turn it off]
should come from monitoring the soil.”
Dr. Melvin D. Campbell

12. WHERE DO THE DATA COME
FROM?
Solar Radiation
Wind
Temp
Humidity
Rain
ZL6 Data Logger
- Solar charging
- Cell enabled
- Data directly to cloud
Soil Moisture

14. STEPS FOR SCHEDULING
IRRIGATION BY SOIL MOISTURE
MONITORING
• Select a monitoring site
• Select a moisture monitoring method
• Set the full and refill points
• Select and use a record-keeping scheme

15. SITE SELECTION
The “Field” average is not needed
Since the “field” is irrigated as a unit,
monitor only one representative site

16. CHARACTERISTICS OF A
REPRESENTATIVE SITE
• Away from the edge
• Healthy, vigorous plants
• No runoff/run-on, good water holding capacity soil
• Representative exposure to irrigation and climatic
conditions

17. ZL6 has GPS so georeferencing is automatic
and shown on ZENTRA Cloud

18. MOISTURE MONITORING:
WHAT TO MEASURE?
Water potential–TEROS 21
Energy state of water in soil
-Is the water available to the plant?
-Will the water run out the bottom?
Water content–TEROS 10, 11, 12
Amount of water in soil
-When to irrigate next
-How much water to add

19. WATER CONTENT VS. WATER
POTENTIAL – 3 SOIL TEXTURES

20. MEASURE AT TWO OR MORE
DEPTHS
Shallow sensor monitors root-
zone moisture
Deeper sensors can show
drainage loss
More than two sensors
needed for reliable water
balance

21. FIRST APPROXIMATIONS OF
FULL AND REFILL POINTS
Water potential basis
Full point is -10 to -30 kPa water potential
Permanent wilt is -1500 kPa water potential
Refill point is around -100 kPa
Water content basis
Full point is water content at -30 kPa
Permanent wilt is water content at -1500 kPa
Refill is water content at -100 kPa
Is different for every soil

22. WATER CONTENT FULL AND REFILL
POINTS FROM MOISTURE RELEASE
DATA

24. KEEP A RECORD
• Show time trends of soil moisture within and below
the root zone
• Show the full and refill points
• ZENTRA Cloud does this for you

25. FOOD PROCESSING WASTE
WATER DISPOSAL ON SANDY LOAM SOIL
0
2
4
6
8
10
12
14
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
6/22/2007 6/29/2007 7/6/2007 7/13/2007 7/20/2007 7/27/2007
Irrigation(mm)
VolumetricWaterContent(m3m-3)
15 cm 30 cm
60 cm Applied Water mm

26. WATER CONTENT: POTATOES

27. WATER POTENTIAL: POTATOES

28. DOES GOOD IRRIGATION
MANAGEMENT PAY?
Yield vs. Water Potential Graph
Site Days in stress Yield (Mg/ha)
9 42 31.47
12 53 32.77
10 44 37.44
11 0 39.67
6 0 40.08
7 16 40.33
30
32
34
36
38
40
42
0 10 20 30 40 50 60
Yield(Mg/ha)
Days below -100 kPa

29. CONCLUSIONS
• Good irrigation management pays, in the
short run and in the long run
• Soil moisture monitoring is the best starting
point for good management
• New water content and potential sensors,
linked with sensor-to-cloud technology
makes irrigation management effective and
simple

30. FUTURE WEBINAR
ADVANCED IRRIGATION MANAGEMENT:
PLANT WATER RELATIONS AND
ATMOSPHERIC DEMAND