Crop Water Demand, Use and Importance of Water Management in Forage Crops
Irriga&on Management Workshop
Western Alfalfa and Forage Symposium, “Producing Forages in a Water-‐Challenged
World”
Reno, NV, December 2, 2015
Dr. Howard Neibling, P.E. Water Management Engineer
University of Idaho
What do we want the irrigation system to do??
• Supply water to meet crop needs (minimal stress) for best crop yield and quality – The right amount of water at the right time – Keep up (a system design issue)
• Match wetted depth to root extraction pattern (minimize deep percolation losses, but enhance development of a deep root zone)
Right amount of water at right time and be able to “keep up”
• Therefore, we need good information about daily crop water use – Seasonal crop water use pattern – Peak use – Variability form year to year
3/30
4/13
4/27
5/11
5/25 6/8 6/2
2 7/6 7/20 8/3 8/1
78/3
19/1
49/2
810
/1210
/26
Date
Winter Grain
Spring Grain
Dry Beans
Potatoes
Field CornSugar Beets
Alfalfa
Tillering
Tillering
Boot - flower
Boot - flower
Flowering
Tuber set
PollinationGermination, Emergence
& Early Growth
Early growth New fall seedings
Timing of Crop ET and Critical Crop Stages for Magic Valley Conditions
How do you get crop water use (ET) information?
• Lysimeter data (measured using water balance)
• Remote Sensing (Metric, EC) • Estimated use based on daily weather data
(historical data for planning and current year data for scheduling) – CIMIS – AgriMet – …
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
5/1 5/31 6/30 7/30 8/29 9/28
Actual ET,in/d
Alfalfa Lysimeter Trial, 2014 Davis, CA
Actual ET" CIMIS PM ETo
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
3/1 3/31 4/30 5/30 6/29 7/29 8/28 9/27 10/27
Actual ET, in/d
Alfalfa Lysimeter Trial, 2015 Davis, CA
Actual ET CIMIS PM ETo
Average 30-Year Alfalfa ET With Cutting, Kimberly
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
3/31 4/14 4/28 5/12 5/26 6/9 6/23 7/7 7/21 8/4 8/18 9/1 9/15 9/29 10/13 10/27
Kim
ber
ly P
enm
an E
stim
ated
ET
, in
/d Max. Pivot Capacity @ 6.5 gpm/ac & 80% AE
Max. Pivot Capacity @8 gpm/ac & 80% AE
What is the relationship between crop water use and alfalfa
production?
What is the relationship between crop water use and alfalfa production?
• Linear increase in yield with increasing water use to estimated peak ET, then drops off
• Slope of line changes with location • At Kimberly, what is an inch of water
worth? – Early season: about 510 lb – Remaining season: 400 lb
Adequate Early-season Water Is Important for Alfalfa Production!
What is an inch of water worth? – Early season: about 510 lb – Remaining season: 400 lb
Alfalfa • Yield proportional to water added (5 inches per ton of
hay) • Irrigate young stands frequently to develop adequate root
depth • Roots will develop to 4 ft + if soil and irrigation
management allow • Irrigate right after harvest to enhance re-growth • Better to stretch water over more acres than to fully
irrigate limited acres
Pivot design should accommodate some uncertainty in peak ET
Yearly water use patterns are quite variable, so irrigating
according to “average” values may not give the best results
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0.45
5/1 5/29 6/26 7/24 8/21 9/18
AG
RIM
ET E
T, in
/d
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Picabo 1992-2007
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0.35
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4/1 5/1 5/31 6/30 7/30 8/29 9/28
Agr
iMet
Est
imat
e E
T, in
/day
Rexburg Alfalfa
92-07 average (29 in) 2007 (38 in) 1992 (25 in)
6 gpm/ac
Moderate Elevation Sites
High Elevation Sites
Mean Alfalfa ET - Kimberly
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
1/0 1/14
1/28
2/11
2/25
3/10
3/24 4/7 4/2
1 5/5 5/19 6/2 6/1
66/3
07/1
47/2
88/1
18/2
5 9/8 9/22
10/6
10/20
AGRI
MRT
ET,
Inch
es/d
ay
200391-02 avg
Max. center pivot rate at 6.9 gpm/ac
Max. Set-Move rate at 9 gpm/ac
The End -- Questions ??
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4/9 5/7 6/4 7/2 7/30 8/27 9/24 10/22
AG
RIM
ET E
T,In
/d
Picabo, 2000
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0.05
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0.35
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0.45
4/9 5/7 6/4 7/2 7/30 8/27 9/24 10/22
AG
RIM
ET E
T,In
/d
Picabo, 2003
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0.35
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0.45
4/9 5/7 6/4 7/2 7/30 8/27 9/24 10/22
AG
RIM
ET E
T,In
/d
Picabo, 2007
Alfalfa Irrigation Considerations • Alfalfa is deep rooted with nearly uniform water extraction
with depth • Pivots need to be run as slow as possible without runoff to
encourage deeper roots • Set-move systems
– Need to return fast enough so that crops are not stressed between sets
– Need to apply only water to re-fill root zone • Seasonally high water table
– Limits root depth – therefore each irrigation must be smaller and irrigations should
occur more often to avoid leaching & stress
Pivot design should accommodate some uncertainty in peak ET
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5/4 5/24 6/13 7/3 7/23 8/12 9/1 9/21
2004
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
5/4 5/24 6/13 7/3 7/23 8/12 9/1 9/21
2007
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
5/4 5/24 6/13 7/3 7/23 8/12 9/1 9/21
2008
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
5/4 5/24 6/13 7/3 7/23 8/12 9/1 9/21
2009