This document discusses improving water efficiency in cool season hay production through better flood irrigation techniques. It recommends irrigating to fill the active root zone without excess runoff by understanding soil water capacity. Proper soil moisture monitoring using the "feel method" can help determine when to irrigate. Measuring irrigation water flow using weirs can improve management. Species selection, grazing management, and fall irrigation are other strategies to enhance water use efficiency. Calculating irrigation time and depth using the irrigator's equation allows for effective water delivery scheduling.

1. WATER EFFICIENCY
IN COOL SEASON HAY
PRODUCTION
Caleb Carter
UW Extension Educator
Master Hay Grower Program
Laramie, WY
March 24, 2015

2. IMPROVING FLOOD
IRRIGATION
EFFICIENCY

3. Goal?

4. Active root zone

5. FLOOD IRRIGATION
• Efficient flood
irrigation
– Almost filling root
zone
– Utilizing or
minimizing runoff

6. WHAT ABOUT THE SOIL?
“…and we can save 700 lira by not taking soil samples!”

7. The water balance

8. Web soil survey
Obtain info on:
• Soil type
• H2O capacity
• infiltration
http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm

9. Available soil moisture
• Field Capacity
• 50% Available
Water
• Permanent
Wilting Point
• MAD

10. Effects of irrigation on
infiltration
Soil Texture
Basic
Infiltration
Rate (in/hr)
Fine sand 0.50 – 0.75
Sandy loam 0.35 – 0.5
Silt loam 0.25 – 0.40
Clay 0.10 – 0.20

11. Management allowable
depletion (MAD)
Take half, leave half…
…works for water too

12. GETTING DOWN TO
BUSINESS

13. FEEL METHOD
• If it makes a ball
and falls apart
when you bounce it
in your hand,
needs irrigation

15. Water use
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
Evapotranspiration
(inches/month)
Mean CU
Max CU
Min CU

16. WATER MEASUREMENT

17. Irrigation water measurement

18. WEIRS
Given: Standard Contracted Rectangular Weir
L = 2 feet
h = 0.40 feet
Find: Q, in cfs
Solution: Refer to Table A7-2 in BoR Water
Measurement Manual, 3rd edition

19. WEIRS

20. Water measurement
• $3 plus shipping
from UW Extension

21. Volume
• Acre-inch: The volume of water required to
cover 1 acre 1-inch deep.
• Acre-foot: The volume of water required to
cover 1 acre 1-foot deep.
• 1 cubic foot = 7.48 gallons = 62.4 pounds
• 1 acre-inch = 3,630 cubic feet = 27,154
gallons
• 1 acre-foot = 12 acre inches = 43,560 cubic
feet = 325,851 gallons

22. Flow
• 1 acre-inch/hour = approximately 450 gallons
per minute = 1 cubic foot per second

23. STRATEGIES

24. Strategies
• Experience/observation
• Gated pipe
• Improving irrigation
management
• Field leveling
• Lining ditches

25. Water use efficiency

26. Cool season grasses

27. Warm season grasses

28. SPECIES SELECTION
Drought resistant
• Orchard grass
• Intermediate
wheatgrass
• Other wheatgrasses
– Can tolerate only
spring water
Less resistant
• Pubescent
wheatgrass
• Intermediate
wheatgrass

29. GRAZING
• Maintain
stubble at 5
to 6 inches
• Avoid
irrigating
while
grazing

30. Boulder watershed study
• Study findings:
– Generally,
applications by
ranchers sufficient to
meet the needs of the
crop

31. Boulder watershed study
• Producer findings:
– Allowed lengthened sets
– Can irrigate larger area
– More even distribution
– Increased yields
– Less labor intensive
– Feel that it is more
efficient and has
increased yields

32. Fall irrigation
Why?
• Increase fall weed
flush
• Can facilitate fall
tillage
• Fall plant growth
– Tiller production
• Leaching of salts
• Storing soil moisture

33. Other considerations…
• Reduced return flows?
– Laramie Basin
• 74 wetlands
• 65% inflows from irrigation
• Most subsurface flows
– Powell, WY example

34. Other considerations…

35. Questions?
Caleb Carter
UW Extension Educator
Goshen County
(307) 532-2436
ccarte13@uwyo.edu

36. IRRIGATION STRATEGIES
Furrow
• Less efficient
• Labor intense
• Soil is the conduit to convey
water as well as the
absorbing surface
• Often requires a catchment
and reuse area at the
bottom of the field
• Water delivery
schedule/amount
Surge
• Can increase efficiency
• Can decrease labor
• Addresses soil as the
conduit
• Can help reduce runoff if
no catchment area
• Can make better use of
water available

37. SURGE IRRIGATION

38. Irrigator’s equation
Qt = Ad
Q = flow rate
t = time
A = area
D = depth

39. Irrigator’s equation
d = Qt/A
Q = Ad/t
t = Ad/Q
A = Qt/d

40. Irrigator’s equation
Given: d = 3 inches
A = 50 acres
Q = 2 cfs
Find: Time required to apply d

41. Irrigator’s equation
Solution: t = dA/Q
1 cfs ≈ 1 ac-in/hr
t = 75 hours
hr
inac
)ac)(in(
t


2
503

42. Irrigator’s equation
Given: t = 36 hours
A = 20 acres
Q = 2 cfs
Find: Depth of applied water, d

43. Irrigator’s equation
Solution: d = Qt/A
1 cfs ≈ 1 ac-in/hr
d = 3.6 inches
ac
)hr)(
hr
inac(
d
20
362 
