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Irrigation water quality

Micah Woods
March 08, 2017

Irrigation water quality

I used these slides for a presentation about irrigation water quality at the Sustainable Turfgrass Management in Asia 2017 conference. I then showed various calculations of the daily soil water balance.

Micah Woods

March 08, 2017
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  1. Irrigation water quality
    Micah Woods
    8 March 2017
    Chief Scientist | Asian Turfgrass Center
    www.asianturfgrass.com

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  2. 1. Salinity and sodium hazard

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  3. 1. Salinity and sodium hazard
    2. Soil moisture content

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  4. 1. Salinity and sodium hazard
    2. Soil moisture content
    3. Daily soil water balance

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  5. Salinity

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  6. The salt in the water is salinity

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  7. The salt in the water is salinity

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  8. As salinity increases, water uptake (growth) decreases

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  9. As salinity increases, water uptake (growth) decreases

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  10. The salt in the water is the most important
    water quality parameter.

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  11. Salinity is measured in two ways
    Total dissolved solids
    By evaporating the water, and measuring what remains, one
    gets total dissolved solids (TDS), reported as mg/L, or ppm.

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  12. Salinity is measured in two ways
    Electrical conductivity
    When there is more salt in the water, it can conduct more
    electricity. The electrical conductivity (ECw
    ) is in units of dS/m.

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  13. Converting from TDS to ECw
    1 dS/m ≈ 640 ppm

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  15. Yesterday at field day

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  16. Yesterday at field day

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  17. Salinity is managed by adding more water than
    the grass can use or the soil can hold.

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  18. This is called a leaching fraction
    2 step process
    First, calculate the leaching requirement (LR). Second,
    calculate the quantity of water to apply.
    Let's imagine we have a water with a TDS of 1,500 ppm. And we
    expect the grass to use (ETc
    ) 4 mm. How much water is
    required for irrigation?

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  19. Leaching requirement
    LR =
    ECw
    5(ECe) − ECw

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  20. Using the leaching requirement
    After we have the LR, then we calculate the quantity of water
    to apply as:
    irrigation =
    ETc
    1 − LR

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  21. Example calculation, step 1
    LR =
    2.3
    5(10) − 2.3 = 0.05

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  22. Example calculation, step 2
    irrigation =
    4
    1 − 0.05 = 4.2

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  23. My favorite reference guide about water
    http://anrcatalog.ucanr.edu/pdf/8009.pdf

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  24. My favorite reference guide about water
    From Harivandi's Interpreting turfgrass irrigation water test results

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  25. Even seashore paspalum dies when salinity is uncontrolled

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  26. Sodium hazard

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  27. If there is too much sodium in the irrigation
    water, the sodium causes deflocculation of the
    soil clay particles. This is not a problem on
    sand rootzones.

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  28. Flocculation and deflocculation of clay

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  29. Chemical compaction

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  30. Check sodium hazard by SAR
    Sodium adsorption ratio (SAR)
    SAR =
    Na

    (Ca + Mg)/2

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  31. Solve a sodium problem by adding gypsum

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  32. Increasing the Ca solves the sodium problem

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  33. From Harivandi's Interpreting turfgrass irrigation water test results

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  34. Additional information

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  35. Additional information

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  36. Things not to worry about
    • bicarbonate

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  37. Not a problem

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  38. Things not to worry about
    • bicarbonate
    • water pH

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  39. Soil water content

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  40. Know three numbers
    1. The volumetric water content (VWC) at field capacity

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  41. Know three numbers
    1. The volumetric water content (VWC) at field capacity
    2. The VWC at the wilting point

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  42. Know three numbers
    1. The volumetric water content (VWC) at field capacity
    2. The VWC at the wilting point
    3. The VWC now

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  43. Measure with a soil moisture meter

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  44. Measure with a soil moisture meter

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  45. Daily soil water balance

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  46. Bangkok, daily soil water balance

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  47. Bangkok, daily soil water balance

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  48. Phuket, daily soil water balance

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  49. Chiang Mai, daily soil water balance

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