Micah Woods
March 08, 2017
2.9k

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.

March 08, 2017

Transcript

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

2. 1. Salinity and sodium hazard

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

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

5. Salinity

6. The salt in the water is salinity

7. The salt in the water is salinity

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

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

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

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.

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.

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

14. Yesterday at ﬁeld day

15. Yesterday at ﬁeld day

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

17. 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?

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

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

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

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

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

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

24. Even seashore paspalum dies when salinity is uncontrolled

25. Sodium hazard

26. 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.

27. Flocculation and deﬂocculation of clay

28. Chemical compaction

29. Check sodium hazard by SAR
SAR =
Na

(Ca + Mg)/2

30. Solve a sodium problem by adding gypsum

31. Increasing the Ca solves the sodium problem

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

35. Things not to worry about
• bicarbonate

36. Not a problem

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

38. Soil water content

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

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

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

42. Measure with a soil moisture meter

43. Measure with a soil moisture meter

44. Daily soil water balance

45. Bangkok, daily soil water balance

46. Bangkok, daily soil water balance

47. Phuket, daily soil water balance

48. Chiang Mai, daily soil water balance