Irrigate More Efficiently Using the Salt Balance

The global pressure for water conservation is felt in every industry, especially in arid countries. In agriculture, the balance can be hard to find.

Identifying the movement of water through soil.
To efficiently manage the irrigation of a crop you must know how much water is put down via irrigation and precipitation, how much is lost via drainage, and how much is lost to evapotranspiration. Salt is also applied and lost with the water, so the salt and water balance are strongly linked. New methods are available for measuring components of the water and salt balance of a crop. In this 30-minute webinar, Dr. Gaylon Campbell, Senior Research Scientist at METER for over 25 years, breaks down how to measure the water and salt balance and how to use these measurements to improve irrigation efficiency.

He discusses:
- Climate change impacts on irrigated agriculture
- Things that can and cannot increase water use efficiency in agriculture
- What the salt balance is
- How the salt balance relates to the water balance
- How to quantify drainage by measuring salt
- Using pore water EC to estimate drainage
- And more

2. IRRIGATE MORE EFFICIENTLY
USING SALT BALANCE
Gaylon S. Campbell, PhD
METER Group, Inc. USA Pullman, WA USA

3. •“Climate change, population growth, and increasing water
scarcity will put pressure on our food supply.” (IPCC)
•“Most of the freshwater (about 70 per cent on average) is used
for agriculture.”
•“It takes between 2000 and 5000 liters of water to produce a person’s daily food.” (FAO )
WATER IN THE NEWS

4. •Minimize waste
•Maximize water-use efficiency
•Help implement and use sustainable practices
WHAT CAN WE DO TO HELP?

5. Rootzone water content – too fast
Salt in groundwater and rivers –too slow
Salt concentration near the bottom of
the root zone –just right
STIRZAKER’S
GOLDILOCKS
PRINCIPLE

6. Inputs: Precipitation,
Irrigation
Losses: Transpiration,
Evaporation, Drainage
Storage: Change in
soil water content
THE WATER BUDGET
TEROS 12 soil moisture,
EC, temperature sensor
ATMOS 41W
Microenvironment Monitor

7. •Salts are in all irrigation water
•Salts and water enter soil
•Water leaves, but salts remain
THE SALT BUDGET

8. ATMOS 41W
WEATHER STATION

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

10. Measure salt as
concentration,
electrical
conductivity, or
osmotic potential

11. Total water potential of soil
depends on salt concentration
(osmotic potential) and soil
matric potential
HIGH SALT
CONCENTRATIONS
STRESS PLANTS

12. CORN GRAIN
YIELD RESPONSE
TO SALT STRESS
Hoffman, G. J., E. V. Maas, T. L. Prichard, and J. L. Meyer
(1983) Salt tolerance of corn in the Sacramento-San
Joaquin Delta of California. Irrig. Sci. 4:31-41

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

14. CROP YIELD RESPONSE TO SALT
SensitiveModerately
Sensitive
Tolerant

15. •Bulk EC
b – The EC measured by in situ sensors
•Pore water or soil solution EC
w - What the
plant “sees”
•Saturation extract EC
e – Saturate the soil with
distilled water, extract the water, and measure
its EC – directly proportional to the salt
content of the soil
THREE MEASURES
OF ELECTRICAL
CONDUCTIVITY
TEROS 12 Water Content
EC & Temperature

16. To get pore water EC
•Suck water out of soil with suction cup
and measure its EC
•Measure bulk EC and bulk dielectric
and calculate with Hilhorst
HOW DO YOU GET EC
w?
????????????????????????
????????????=
????????????????????????
???????????? ????????????
????????????
????????????
????????????−????????????0
EC
w = pore water EC
EC
b = bulk EC
ε
w = water dielectric
ε
b = bulk dielectric
ε
0 = dry dielectric

17. SOME TOOLS
ES-2 Water EC &
Temperature
ATMOS 41W TEROS 12 Soil Water
EC & Temperature
ZL6 Logger Connected
to ZENTRA Cloud

18. •The irrigation water EC
•The EC
w in the root zone so you can avoid stressing the crop
•The EC
w below the root zone so you can compute the rate of drainage
NOW WE CAN
CONTINUOUSLY KNOW

19. •Defined as the ratio of drainage water to applied water: LF = D
d/D
i
•Can use it to compute drainage required for a particular irrigation water quality:
LF = EC
i/EC
w
•If EC
i were 0.6 dS/m and EC
w were 3 dS/m, then LF would be 0.2;
1/5 of the water would need to drain to maintain productivity
MAINTAINING SOIL PRODUCTIVITY
LEACHING FRACTION

20. •The TEROS 12 measures water content
and bulk EC (EC
b )
•ZENTRA Cloud converts that to pore
water EC (EC
w )
•EC
w at bottom of root zone is
Stirzaker’s Goldilocks measurement
Gives
•Crop suitability
•Crop loss from salinity
WHAT CAN WE
DO WITH THIS?

21. GRACE, ID: WHEAT

22. •The TEROS 12 measures water content and bulk EC (EC
b )
•ZENTRA Cloud converts that to pore water EC (EC
w )
•ES-2 measures irrigation water EC (EC
i)
•Rearrange leaching fraction equation to give D
d=D
i(EC
i/EC
w) so, from the EC
measurements and knowing depth of water applied, you can calculate the
depth of drainage
WHAT ELSE CAN WE DO?
D
d – depth of drainage water
D
i – depth of irrigation water
EC
i – irrigation water EC
EC
w – pore water EC in soil

23. •Correctly managing water for irrigation requires a knowledge of
soil water content and soil salt content
•The pore water EC within and below the root zone is “just right”
as the long-term management tool for irrigated agriculture
•METER provides the right measurements for modern irrigators
to choose the right crops and manage water sustainably
CONCLUSIONS

24. QUESTIONS?
Thank you for your time