Managing salts: Why you should care more Mismanagement of salt applied during irrigation ultimately reduces production—drastically in many cases. Irrigating incorrectly also increases water cost and the energy used to apply it. Understanding the salt balance in the soil and knowing the leaching fraction, or the amount of extra irrigation water that must be applied to maintain acceptable root zone salinity is critical to every irrigation manager’s success. Yet monitoring soil salinity is often poorly understood. Measure EC for consistently high crop yields In this webinar, world-renowned soil physicist Dr. Gaylon Campbell teaches the fundamentals of measuring soil electrical conductivity (EC) and how to use a tool that few people think about—but is absolutely essential for maintaining crop yield and profit. Learn: - The sources of salt in irrigated agriculture - How and why salt affects plants - How salt in soil is measured - How common measurements are related to the amount of salt in soil - How salt affects various plant species - How to perform the calculations needed to know how much water to apply for a given water quality

2. SOIL ELECTRICAL
CONDUCTIVITY
MANAGING SALTS FOR SUSTAINED
HIGH YIELDS
Gaylon S. Campbell, PhD
METER Group, Inc. USA

3. THE COST OF SALT IN
IRRIGATED AGRICULTURE
• Sins of past management
practices
• Threats to the future
• Cost in lost production

4. GOLDILOCKS PRINCIPLE
Stirzaker’s Goldilocks Principle
• Root zone water content
- Too fast
• Salt in groundwater and rivers
- Too slow
• Salt concentration near the
bottom of the root zone
- Just right

5. THE PROBLEM
• Salts are in all irrigation
water
• Salts and water enter soil
• Water leaves, but salts
remain

6. ADDITIONAL SALT SOURCES
• Fertilizer is applied to crops,
some stays
• Groundwater also contains
salt
• Water and salts flow upward
from shallow water tables
• Water leaves, but salts stay

7. HIGH SALT CONCENTRATIONS
STRESS PLANTS
• Salt concentrates as the soil dries
• Total water potential of soil
depends on:
– Salt concentration (osmotic potential)
– Soil matric potential

8. CROP SENSITIVITY TO SALT
Sensitive
Moderately
Sensitive
Moderately
Tolerant Tolerant
almond alfalfa olive barley
apple broccoli red beet Bermuda grass
avocado cabbage ryegrass cotton
bean corn safflower date palm
carrot cucumber soybean sugar beet
grapefruit grape wheat
lemon lettuce wheatgrass
okra peanut wildrye
onion potato
orange radish
peach rice
plum sugarcane
strawberry tomato

9. CLASSIFICATION OF
SALT SENSITIVITY
Sensitive Moderately
Sensitive
Tolerant
Sensitive Moderately
Sensitive
Tolerant
Sensitive Moderately
Sensitive
Tolerant

10. SALT CONCENTRATION VS.
EC AND OSMOTIC POTENTIAL
• Salt in water increases
its EC
• Salt decreases water
availability to plants
– More negative osmotic
potential

11. THREE MEASURES OF EC
• Bulk (ECb)
– EC measured by in situ sensors
• Pore water or soil solution (ECw)
– What the plant “sees”
• Saturation extract (ECe)
– Saturate the soil with distilled water, extract the water,
and measure its EC
– Directly proportional to the salt content of the soil
TEROS 12
Water content,
EC, & temp

12. 𝑘𝑘𝑔𝑔𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
𝑚𝑚𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤
3 ×
𝑚𝑚𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤
3
𝑚𝑚𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
3 =
𝑘𝑘𝑔𝑔𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
𝑚𝑚𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
3
ECw
(=ECe at sat.)
Water
content
Salt
content
× =
SATURATION EXTRACT EC (ECE)
FUNDAMENTAL PROPERTY OF SOIL

13. PROCESSES THAT AFFECT
SALT IN SOIL
• Redistribution
– Water moving to deeper soil depths
– Water and salt content change together
• Evapotranspiration
– Water evaporating from the soil or plant
– Water content changes, but salt content stays constant

14. EC DURING REDISTRIBUTION

15. EC DURING EVAPORATION

16. WHY IS SOIL EC LOWER THAN
WATER EC?
Water Saturated Soil Field Capacity
1.Cross section for flow is smaller in soil
2.Flow path is longer in soil
ECb = ECw
ECb = ECw/3 ECb = ECw/10

17. RELATING ECW TO ECB
• Pore water EC will always be greater
than ECb
• At low water content, the multiplier is
very large
• Water content must be known to
determine ECw from ECb
• Texture doesn’t play a big role in the
relationship
• ECe = ECw * saturation VWC

18. MAINTAINING SOIL
PRODUCTIVITY
LEACHING FRACTION
• Defined as the ratio of drainage water to applied water
– LF = Dd/Di
• Can use it to compute drainage required for a particular irrigation
water quality
– LF = ECi/ECe
• If ECi = 0.3 dS/m, and ECe = 3 dS/m, then LF = 0.1
– 10% of the water would need to drain to maintain productivity

19. EC OF NATURAL WATERS
WESTERN USA
River EC (dS/m)
Columbia (Wenatchee) 0.15
Snake (Minidoka) 0.41
Sacramento (Tisdale) 0.16
Rio Grande (El Paso) 1.16
Pecos (Carlsbad) 3.21
Colorado (Yuma) 1.06

20. THE TOOLS
ES-2
Water EC & temp
ZL6
Data logger connected
to ZENTRA Cloud
TEROS 12
Soil water EC & temp

21. WHAT WE CAN DO
• TEROS 12 measures water content and bulk EC (ECb)
• ZENTRA Cloud converts that to pore water EC (ECw)
• Water content * ECw = saturation extract EC (ECe)
• ECe at bottom of root zone is Stirzaker’s Goldilocks measurement
• Gives:
– Crop suitability
– Crop loss from salinity
– Leaching fraction (with irrigation water EC)
• ECi = 0.3, ECe = 3, LF = 0.4/4 = 0.1 Sensitive
Moderately
Sensitive
Tolerant

22. EC DATA UNDER WHEAT
GRACE, IDAHO

23. CONCLUSIONS
• Mismanagement of salt in irrigated agriculture is costly
• Monitoring the saturation extract EC at the bottom of the root
zone is “just right” as a long-term management tool for irrigated
agriculture
• METER has the tools to provide the right measurements for
modern irrigators to choose the right crops and manage water
sustainably

24. QUESTIONS