Why overwatering is causing you problems. Just like a thermostat can be set optimally for comfort without wasting heat, the latest advances in sensor technology can do the same for plants: keep them comfortable, without wasting water. This means you can have higher quality and yield while reducing problems caused by overwatering such as disease or the need to reapply expensive nutrients that have been flushed away. Better management--better plant performance. Join Dr. Colin Campbell as he explores the latest water management research and real world examples to answer the questions: Does water management work? What are challenges and best practices? And what should we do next? Discover: - The role water plays in managed ecosystems. - How using measurement technology like soil water potential, soil water content, electrical conductivity, and temperature can show impacts of management. - How to deploy these sensors effectively in high-dollar ecosystems. - What the interplay is between environmental variables like evapotranspiration and soil water. - How combining these variables can inform water management. - How overwatering impacts disease and critical nutrients in the root zone.

2. WATER MANAGEMENT
3 TOOLS YOU MAY BE MISSING
Colin S. Campbell, PhD
METER Group, Inc.

3. IGNAZ SEMMELWEIS AND
PUERPERAL FEVER
Source: en.wikipedia.org/wiki/Ignaz_Semmelweis

4. IRRIGATION MANAGERS
The intention of irrigation systems is to get healthy ‘crops’ and
optimal yield (performance)
The goal is to get this while minimizing water, fertilizer, labor, herbicides, etc.
They get the very thing they are trying to avoid
What they get:
• Higher water use
• Lower nutrient availability
• Higher weed pressure
• More labor

5. CASE STUDIES
WATER NOT IN BALANCE

6. SPORTS TURF
• 12 inches of ASTM Spec soil
• Designed perched water table
GOAL
• #1: Keep grass beautiful for gameday
• Playing surface optimal for
football players
• Optimize inputs
• Reduce invasive weed pressure (Poa)

7. FIELD WATER CONTENT
NORTH – SUMMER
• Root zone optimal range ~ 7 to 12%
6 in
12 in
2 in

8. • Root zone optimal range ~ 7 to 12%
6 in
12 in
2 in
FIELD WATER CONTENT
SOUTH – SUMMER

9. FIELD NUTRIENTS
SUMMER
Optimal:
2 to 5 mS/cm
Tap water
LES
2-inch North
2-inch South
2-inch Silt loam Field
Pore Water Electrical Conductivity (ECp)

10. TURFGRASS PROBLEMS
• Low nutrient availability limits canopy greenness
• Excess water favors annual bluegrass (Poa) over
perennial bluegrass
• Poa forms much weaker soil structure
• Developed shallow root systems with excessive water

11. OUTDOOR CANNABIS
IRRIGATION FIELD SETUP
Details
• 1 m plant spacing/transplanted
from greenhouse
• 2 m between rows
• Drip tape irrigation system under
black plastic mulch (Open Sprinkler)
• ~30 cm spacing, 0.5 l h-1 drip
• Silt loam soil
• Sensors at 15, 30, and 60 cm
Observations
• Hot, dry spring/summer
• limited latent soil water
• pre-planting irrigation moistened
soil to sensor installation depth
• Security fence many have created
microclimates
• Irrigator followed sensor readings
but rarely adjusted timing

12. SOIL WATER CONTENT
30 CM DEPTH

13. OUTDOOR CANNABIS
IRRIGATION PROBLEMS
How much water was applied daily?
• 0.375 mm h-1 overall application rate
(30 min on/30 min off)
• Two to three cycles per day typical
• 1 cycle = 1 h
• Total applied < 2 mm d-1 the whole
season
• Two extended irrigation events late
in season
How much water was required?
(Estimated from daily pictures)
• Much less than 1 mm at planting
• Increased quickly to full ETo by early
August
• Applied irrigation woefully short of
requirement
• Irrigator observed ‘muddy’ conditions
under plastic
• Challenging infiltration under dry
conditions

14. TOOLS YOU MIGHT BE MISSING

15. VISION FOR IRRIGATION
Irrigation is simple: you must know when to turn the water on and
when to turn it off
The answer to THAT question is the hard part
To answer the irrigation question, you must know three things:
1. How much water the crop used
2. The current availability of water in the soil
3. Total water available

16. TOOLS THAT HELP
How much water are my plants using daily?
• Evapotranspiration – the amount of water lost due to evaporation from
the soil and transpiration from the plant canopy
Is the water in the soil optimally available for plant growth?
• Soil water potential – like temperature shows thermal comfort range
regardless of the size of room, water potential determines if water is
available to plants no matter the soil type
How much water is freely available to the plant?
• Moisture release curve – relationship between water potential and
water content defines available water envelope

17. TOOL 1
EVAPOTRANSPIRATION

18. HOW MUCH WATER WAS USED?
PENMAN-MONTEITH EQUATION
𝜆𝜆𝐸𝐸 =
𝑠𝑠 𝑅𝑅𝑛𝑛 − 𝐺𝐺 + 𝛾𝛾∗
𝜆𝜆𝑔𝑔𝑣𝑣𝐷𝐷/𝑃𝑃𝑃𝑃
𝑠𝑠 + 𝛾𝛾∗
λ𝐸𝐸𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = kc ∗ λ𝐸𝐸0
Reference crop: 12 cm grass
Assumptions  λEo

19. HOW TO MEASURE ETO
Evapotranspiration (ET)

20. ESTIMATED CROP WATER LOST
ETO
6 mm d-1
4 mm d-1
5 mm d-1
• kc still needs to be calculated and multiplied in

21. REFERENCE ET
KEEPS YOU GOING IN THE SAME DIRECTION

22. BUT IS THAT WHERE YOU WANT TO BE?
REFERENCE ET

23. PRACTICE FIELD
ETO ONLY CONTROL
Native silt loam soil

24. PRACTICE FIELD
WATER CONTENT

25. TOOL 2
SOIL WATER POTENTIAL

26. SOIL WATER POTENTIAL
IS WATER AVAILABLE?
Measuring water in soil is essential to
good management
• Ideally, we’d like to keep water in the soil at an
optimum level for green, healthy plants
There are two ways to measure water in soil
• Water content
• The amount of water in soil
• Usually read in a percent (“23% water content”)
• Water potential
• Energy level
• How easy it is for a plant to pull that water from soil

27. Temperature defines human comfort level,
not heat content
• Heat content – the amount of heat in a room
• Temperature – the energy state of heat in a room
• Temperature defines your comfort level
Soil water potential defines plant comfort,
not water content
• Water content – how much water is there, but can a plant get it?
• Water potential – the water ‘thermometer’ of the plant root zone
• We can KNOW if the plant can access water in ANY soil
WHAT DEFINES WHEN CROPS
HAVE OPTIMAL WATER?

28. OPTIMAL SOIL WATER POTENTIAL
Sterling Taylor, 1972, Physical
Edaphology:The physics of
irrigated and non-irrigated soils
-30 to -50 kPa

29. COMBINING ETO AND
WATER POTENTIAL
Soil water potential
Evapotranspiration (ET)

30. REFERENCE ET AND
WATER POTENTIAL

31. PRACTICE FIELD
ETO ONLY CONTROL
Native silt loam soil, water potential goal  -20 to -100 kPa

32. PRACTICE FIELD WATER POTENTIAL
Water content
Water potential

33. AVAILABLE SOIL WATER
TEROS 21 GEN 2
• Ψ range: -0.5 to -105 kPa

34. POTATO-WATER RELATIONS
Location: Grace, Idaho

35. STRESS AND YIELD
POTATOES
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
Location: Grace, Idaho

36. ETO AND PRECIP/IRRIGTAION
Location: Rexburg, Idaho

37. SOIL WATER POTENTIAL
15/30 CM
Location: Rexburg, Idaho

38. TOOL 3
MOISTURE RELEASE CURVE
HOW MUCH WATER IS FREELY
AVAILABLE TO THE PLANT?

39. AVAILABLE WATER
Sand
Silt loam

40. WHAT IS A MOISTURE
RELEASE CURVE?
• Compares the amount of water with
what’s available for the plant to use
• As a soil dries, removing (releasing)
water becomes harder
• A moisture release curve describes
how much available water you have
(kPa)

41. OPTIMAL MOISTURE RANGE
15 cm deep layer: Maximum of 12 mm of irrigation to fill up profile

42. HOW TO APPLY A MOISTURE
RELEASE CURVE
1. Determine upper and lower limit of water potential
• Individual crop data shown earlier
2. Find water content values for upper and lower
water potential limits
3. Determine plant root zone depth (zroot)
4. Take difference in water content and multiply by rooting depth
Max Irrigation = 𝑉𝑉𝑉𝑉𝑉𝑉𝑢𝑢𝑢𝑢 − 𝑉𝑉𝑉𝑉𝑉𝑉𝑙𝑙𝑙𝑙𝑙𝑙 𝑧𝑧𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
= 0.16 − 0.08 × 15 cm = 1.2 cm or 12 mm

43. ESTIMATED CROP WATER LOST
ETO
6 mm d-1
4 mm d-1
5 mm d-1

44. RESULTS
Cannabis irrigation much less than envelope need

45. SUMMARY
• Irrigation may be hurting the very plants we’re trying to help
• Three potential tools that could improve plant health and
resource constraints
• Evapotranspiration is a great start but not enough
• Combining water potential with ETo can keep irrigation
“between the lines”
• Moisture release curves show the amount of water to apply in
the optimal zone

46. QUESTIONS?
Colin S. Campbell, PhD
Senior Research Scientist
www.linkedin.com/in/colin-campbell-meter
METER Group,Inc.
2365 NE Hopkins Ct, Pullman, WA 99163
T 509.332.5600
E sales.environment@metergroup.com
W www.metergroup.com