The document summarizes a study on the effects of limiting water on alfalfa growth and yield in Wyoming. It found that limiting irrigation levels to 25%, 50%, and 75% of full crop water requirements (1.0 ETc) significantly reduced alfalfa dry matter yields compared to the 1.0 ETc treatment. Total dry matter yields were highly correlated with actual crop evapotranspiration. Water use efficiency, the ratio of dry matter yield to water used, decreased with lower irrigation levels.

1. Effects of Limiting Water
on Growth, Development
and Yield of Alfalfa
(Medicago sativa L.)
Grown in the Big Horn
Basin, Wyoming
Caleb Carter, M.S. Candidate

2. Outline
• Importance of alfalfa
• Agricultural water use
• Objectives
• Methodology
• Results
• Conclusions
A. Polvere, 2012

3. Alfalfa
(Medicago sativa L.)
• Queen of forages
• Introduced to U.S.
around 1850
• C3 perennial
legume
• Has a high water
use
(California Alfalfa and Forage Association, 2004)
(Russelle, 2001)

4. Alfalfa
Production
in Wyoming
1,750
1,500
1,250
1,000
750
500
250
0
1950 1960 1970 1980 1990 2000 2010
Production (t y-1 x 1000)
Wyoming Crop Production
Alfalfa
Hay
Corn
Sugarbeet
Wheat
1,800
1,500
1,200
900
600
300
0
1950 1960 1970 1980 1990 2000 2010
Revenue ($ x 100,000)
350
300
250
200
150
100
50
0
1950 1960 1970 1980 1990 2000 2010
Ha Harvested (x1000)
Year (USDA NASS, 2012)

5. Municipal,
Industrial,
etc., 15%
Agriculture,
85%
(USDA NASS, 2012)

6. Definitions
• Evapotranspiration (ET) – The sum of
evaporative losses of water from the soil
surface (evaporation) and from the canopy
(transpiration).
• Reference evapotranspiration (ETo) –.
Evapotranspiration rate from a reference
surface not short of water. Usually a
hypothetical alfalfa or grass plant with
specific characteristics.
• Crop evapotranspiration (ETc) – (Same as
crop water use) Evapotranspiration from
excellently managed, large, well-watered
fields that achieve full production under the
given climatic conditions.
• Water Use Efficiency (WUE) – Ratio
between yield and the amount of water
used to produce that yield.
푊푈퐸 =
푒푐표푛표푚푖푐 푦푖푒푙푑
푤푎푡푒푟 푢푠푒푑 (퐸푇푐 )
A. Polvere, 2012

7. Study Objectives
1. Determine alfalfa’s water use (ETc) and
water use efficiency (WUE) for conditions
in the Big Horn Basin, Wyoming.
2. Quantify the effects of limiting water on
the growth and forage quality of alfalfa.
3. Determine the economic impact of
irrigation scheduling recommendations.

8. METHODOLOGY

9. UW Research and Extension Center,
Powell, WY (PREC)
• 44° 45‘ 30” N, 108° 46‘ 36” W, 1344 masl
• Mean air temp: 8 to 10 °C
• Rainfall: avg. 173 mm
• 125 days frost free period
• Well drained Garland Loam (Fine-loamy over sandy or sandy-skeletal,
mixed, superactive, mesic Typic Haplargids)

10. Experimental Design:
Strip Plot – planted June 7, 2011
0.25ETc 0.50ETc 0.75ETc 1.00ETc
1 2 5 6 7 8 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 6 7
-------------------------------- 6.75 m --------------------------------
Zone 13
Neutron probe Shaw Mountaineer Lander acces tube Watermarks
--------- 11.5 m ---------
-------------------------------------------------- 46 m --------------------------------------------------
3 4 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11
------- 2.25 m --------
Road
12 4 5 8 9 10 11 12
Zone 14 Zone 15 Zone 16
Main treatments – Irrigation:
• 6.75 m wide x 46 m long
• 1.0 ETc, 0.75 ETc, 0.5 ETc and
0.25 ETc
Sub treatments – Alfalfa Varieties:
• 2.25 m wide x 11.5 m long
• Shaw, Lander and Mountaineer

11. Irrigation
• Subsurface Drip Irrigation (SDI)
• Computerized control
• 16 independent zones
• Fertigation

12. Alfalfa Cultivars
Lander
Developed:
• University of
Wyoming
Characteristics:
• Resistant to
Brown Root Rot
Fall Dormancy: 3
Shaw
Developed:
• Montana State
University/
NRCS Bridger
Plants Center
Characteristics:
• Dryland variety
Fall Dormancy: 3
Mountaineer
Developed :
• Forage Genetics
International,
Nampa, Idaho
Characteristics:
• Multifoliate leaf
expression
Fall Dormancy: 4
(Ditterline et al., 2001)
(R. Groose, 2008)

13. Automated Weather Station
UW Res & Ext Center, Powell, WY
www.WAWN.net
ETo Calculation using the ASCE Modified Penman Monteith Equation

14. ASCE Equation
ETo=
0.408Δ Rn−G +γ
퐶푛
T+273
U2 es−ea
Δ+γ 1+퐶푑U2
Where:
• ETsz = standardized reference crop evapotranspiration for short (ETos) or tall (ETrs) surfaces
(mm d-1 for daily time steps or mm h-1 for hourly time steps),
• Rn = calculated net radiation at the crop surface (MJ m-2 d-1 for daily time steps or MJ m-2 h-1
for hourly time steps),
• G = soil heat flux density at the soil surface (MJ m-2 d-1 for daily time steps or MJ m-2 h-1 for
hourly time steps),
• T = mean daily or hourly air temperature at 1.5 to 2.5-m height (°C),
• u2 = mean daily or hourly wind speed at 2-m height (m s-1),
• es = saturation vapor pressure at 1.5 to 2.5-m height (kPa), calculated for daily time steps as
the average of saturation vapor pressure at maximum and minimum air temperature,
• ea = mean actual vapor pressure at 1.5 to 2.5-m height (kPa),
• Δ = slope of the saturation vapor pressure-temperature curve (kPa °C-1),
• γ = psychrometric constant (kPa °C-1),
• Cn = numerator constant that changes with reference type and calculation time step (K mm s3
Mg-1 d-1 or K mm s3 Mg-1 h-1) and
• Cd = denominator constant that changes with reference type and calculation time step (s m-1).
• Units for the 0.408 coefficient are m2 mm MJ-1.
(ASCE-EWRI, 2005)

15. Irrigation Calculations
• Crop water use (ETc): 퐸푇푐 = 퐾푐 × 퐸푇표
• Available Water (AW): 퐴푊 = 퐹퐶 − 푊푃
• Plant Available Water (PAW): 푃퐴푊 =
퐴푊 × 푅푍
• Allowable Depletion (AD): 퐴퐷 = 푃퐴푊 ×
푀퐴퐷
• Soil moisture depletion = PAW – ETc
• Irrigation triggered when the soil moisture
depletion<AD
A. Polvere, 2012

16. Soil Water Balance

17. Water Balance
• Daily soil water balance – measure water in and out:
퐸푇퐶,푖 = 퐼푁,푖 + 푃푖 − 푅푂푖 − 퐷푃푖 + 퐶푅푖 ± (퐷푖−1 − 퐷푖 )
– D (mm) soil water content assuming i is the current
day and i−1 is the previous day
– P (mm) daily precipitation
– RO (mm) runoff
– IN (mm) net irrigation depth
– CR (mm) capillary rise
– ETC (mm) crop evapotranspiration
– DP (mm) is the deep percolation
퐸푇퐶,푖 = 퐼푁,푖 ±(퐷푖−1 − 퐷푖 )
(Allen et al., 1998)

18. Actual Water Use (ETa)
• Actual water use only
measured for the 2nd
and 3rd cuttings
• Used Neutron Probe:
– Releases neutrons at
high speed
– Collide with H protons,
return thermalized
– Measurements taken at
5 depths:
• 20, 40, 60, 80 and 100 cm
http://www.rwma.com

19. Sample Neutron Probe Reading
0
20
40
60
80
100
7/23/12
0 5 10 15 20 25 30
Depth (cm)
% Moisture
Full
75%
50%
25%

20. Estimated ETc
• Water use estimated for
all cuttings as:
– ETc = Kc x ETo
• Used ETo from the
weather station and
crop coefficients (Kc)
calculated from actual
weather data.

21. WATERMARK
Sensors
• For irrigation scheduling purposes only
• Measure soil electric conductivity (EC), relate it
to the matric potential of the soil (cb)
• 4 depths:
o 15 cm
o 30 cm
o 60 cm
o 90 cm

22. Nutrient Quality
o DM – Dry Matter
o ADF – (Acid Detergent Fiber) cellulose + fiber + lignin
o NDF – (Neutral detergent fiber) total fiber or cell wall
fraction
o CP – Crude protein
o TDN – Total Digestible Nutrients
o RFV – Relative Feed Value
http://www.foss.dk/
Measured with Near Infrared
Reflectance Spectroscopy (NIRS)

23. EFFECTS OF LIMITING WATER ON
WATER USE AND WATER USE
EFFCIENCY OF ALFALFA

24. Weather
2011 and 2012 weather compared to the long
term average (LTAvg)
Max Temp (°C) Min Temp (°C) Precipitation (mm)
LTAvg 2011 2012 LTAvg 2011 2012 LTAvg 2011 2012
Jan 0.3 -0.5 4.7 -13.4 -12.2 -9.2 4.8 1.8 0.5
Feb 3.1 -2.3 3.5 -11.1 -14.8 -9.3 2.8 2.0 3.8
Mar 9.4 8.9 16.3 -5.8 -4.8 -1.4 7.1 6.4 10.7
Apr 14.6 11.9 17.9 -0.9 -1.8 1.2 12.7 26.3 4.8
May 19.5 15.1 20.2 4.9 4.2 4.5 37.1 78.0 20.1
Jun 24.8 24.5 29.4 9.0 8.5 11.3 33.3 6.1 8.1
Jul 29.7 32.5 32.9 11.9 13.5 14.4 22.1 1.3 4.6
Aug 29.3 31.1 30.5 10.5 11.9 11.7 11.9 9.9 0.5
Sep 22.7 25.9 26.1 5.1 6.7 7.6 17.0 12.7 2.5
Oct 15.0 16.9 14.1 -1.1 2.2 -0.5 15.5 35.8 5.1
Nov 6.7 5.6 8.3 -7.3 -7.4 -5.6 5.1 6.9 2.3
Dec 0.4 -0.4 0.7 -13.1 -12.0 -11.3 3.8 2.0 2.5
Average 14.6 14.2 17.1 -0.9 -0.4 1.1 Total 176 189 66

25. 2012 Dry Matter Yield
7000
6000
5000
4000
3000
2000
1000
0
8000
6000
4000
2000
100% 75% 50% 25%
DM (kg ha-1)
a) 1st Harvest
a‡
a
b
b
7000
6000
5000
4000
3000
2000
1000
0
b) 2nd Harvest
a
b
c
d
8000
6000
4000
2000
100% 75% 50% 25%
7000
6000
5000
4000
3000
2000
1000
0
c) 3rd Harvest
8,000
6,000
4,000
2,000
100% 75% 50% 25%
DM (kg ha-1)
Irrigation Treatment
a
b
c
d
7000
6000
5000
4000
3000
2000
1000
0
d) 4th Harvest
a a
b
8000
6000
4000
2000
100% 75% 50% 25%
Irrigation Treatment
b
DM= 21.48ETe - 284
n = 45; R² = 0.58
0
0 100 200 300
DM Yield (kh ha-1)
ETe (mm)
DM = 38.12xETa- 1212.7
n = 45; R² = 0.82
0
0 100 200
DM Yield (kg ha-1)
ETa (mm)
DM = 17.32ETe + 609.33
n = 46; R² = 0.83
0
0 100 200 300
DM Yield (kg ha-1)
ETe (mm)
DM = 19.47ETe - 110.18
n = 46;R² = 0.72
0
0 100 200
DM Yield (kg ha-1)
ETa (mm)
‡Different letters within each harvest indicate significant difference (p<0.05) between irrigation treatments.

26. 2012 Total Dry Matter Yield
20000
16000
12000
8000
4000
0
e) Total Harvest
b
c
25000
20000
15000
10000
5000
100% 75% 50% 25%
DM (kg ha-1)
Irrigation Treatment
d
a‡
DM = 22.32ETc - 404.15
n = 46;R² = 0.83
0
0 200 400 600 800
DM Yield (kg ha-1)
ETc (mm)
‡Different letters within each harvest indicate significant difference (p<0.05) between irrigation treatments.

27. Water Use of Alfalfa
Actual vs. Estimated ETc and WUE
Water Use Efficiency
Cut 2
R2 = 0.94
Cut 3
R2 = 0.96
5
4
3
2
1
0
0 1 2 3 4 5
Actual WUE (kg m-3)
Estimated WUE (kg m-3)
Water Use
Cut 2
R² = 0.99
Cut 3
R² = 0.99
250
200
150
100
50
0
0 50 100 150 200 250
Actual ETc (mm)
Estimated ETc (mm)

28. 100%
1st
Harvest
2nd
Harvest
3rd
Water Use (ETc)
Harvest
4th
Harvest Season
Date 6-June§ 12-July 21-Aug 11-Oct
WB 146 217
ASCE-PM 231 142
Total 231 146 217 143 737
75%
1st
Harvest
2nd
Harvest
3rd
Harvest
4th
Harvest Season
Date 6-June 12-July 21-Aug 11-Oct
WB 111 146
ASCE-PM 173 103
Total 173 111 146 103 533
50%
1st
Harvest
2nd
Harvest
3rd
Harvest
4th
Harvest Season
Date 6-June 12-July 21-Aug 11-Oct
WB 84 101
ASCE-PM 116 70
Total 116 84 101 70 371
25%
1st
Harvest
2nd
Harvest
3rd
Harvest
4th
Harvest Season
Date 6-June 12-July 21-Aug 11-Oct
WB 50 48
ASCE-PM 58 35
Total 58 50 48 35 191
• §First growth period assumed to begin on April 1st

29. 2012 Water
Use and
WUE
250
200
150
100
50
0
5
4
3
2
1
0
100% 75% 50% 25%
a a b
100% 75% 50% 25%
WUE kg m-3
Irrigation Treatment
1st cutting
2nd cutting
3rd cutting
4th cutting
1st Harvest
2nd Harvest
3rd Harvest
4th Harvest
a
b
a b
a‡
• Larger variation in
WUE for the 2nd and
3rd cuttings, in the
middle of the season.
• Fully irrigated
treatment showed
higher WUE early in
the season.
Water Use (mm)
‡Different letters within each harvest indicate significant difference (p<0.05) between irrigation treatments.

30. EFFECTS OF LIMITING WATER ON
GROWTH AND FORAGE QUALITY OF
ALFALFA

31. Dry Matter
Production
5000
4000
3000
2000
1000
0
4/16 5/31 7/15 8/29 10/13
Yield (kg ha-1)
Shaw
0.25ET
0.50ET
0.75ET
1.00ET
5000
4000
3000
2000
1000
0
4/16 5/31 7/15 8/29 10/13
Yield (kg ha-1)
Mountaineer
5000
4000
3000
2000
1000
0
Lander
4/16 5/31 7/15 8/29 10/13
Yield (kg ha-1)
Date
• Mountaineer showed
better yield for fully
irrigated.
• Shaw showed better yield
in deficit treatments.

32. 2012 Forage Quality
31%
29%
27%
25%
23%
21%
19%
17%
15%
% Crude Protein
1st Harvest 2nd Harvest 3rd Harvest 4th Harvest
100%
75%
50%
25%
95%
94%
93%
92%
91%
90%
40%
30%
20%
10%
% Dry Matter
% Acid Detergent Fiber
1st Harvest 2nd Harvest 3rd Harvest 4th Harvest
100%
75%
50%
25%
50%
40%
30%
20%
10%
% Neutral Detergent Fiber
1st Harvest 2nd Harvest 3rd Harvest 4th Harvest
100%
75%
50%
25%
89%
1st Harvest 2nd Harvest 3rd Harvest 4th Harvest
100%
75%
50%
25%

33. 2012 Forage Quality
90%
80%
70%
60%
50%
40%
% Total Digestible Nutrients
1st Harvest 2nd Harvest 3rd Harvest 4th Harvest
100%
75%
50%
25%
250
220
190
160
130
100
Realtive Feed Value
1st Harvest 2nd Harvest 3rd Harvest 4th Harvest
100%
75%
50%
25%
• USDA hay quality guidelines†:
Quality Grade ‡RFV ADF % NDF % §TDN-100% TDN-90% Crude Protein %
Supreme >185 <27 <34 >62 >55.9 >22
Premium 170-185 27-29 34-36 60.5-62 54.5-55.9 20-22
Good 150-170 29-32 36-40 58-60 52.5-54.5 18-20
Fair 130-150 32-35 40-44 56-58 50.5-52.5 16-18
Low <130 >35 >44 <56 <50.5 <16
†(Oregon Hay and Forage Association).

34. IRRIGATION SCHEDULING:
POTENTIAL ECONOMIC
IMPLICATIONS FOR THE PRODUCER

35. 2012
WATERMARKs
40
30
20
10
0
300
250
200
150
100
50
0
4/2 4/17 5/2 5/17 6/1 6/16 7/1 7/16 7/31
Irrigation amount
(mm)
Matirc Potential (cb)
a) 100%
40
30
20
10
0
300
250
200
150
100
50
0
4/2 4/17 5/2 5/17 6/1 6/16 7/1 7/16 7/31
Irrigation amount
(mm)
Matirc Potential (cb)
b) 75%
40
30
20
10
0
300
250
200
150
100
50
0
4/2 4/17 5/2 5/17 6/1 6/16 7/1 7/16 7/31
Irrigation Amount
(mm)
Matirc Potential (cb)
c) 50%
40
30
20
10
0
300
250
200
150
100
50
0
d) 25%
4/2 4/17 5/2 5/17 6/1 6/16 7/1 7/16 7/31
Irrigation Amount (mm)
Matirc Potential (cb)
Date
15 30 60 90 Irrigation Depth (mm)
• Soil moisture present
at the beginning of the
season.
• Reaction to irrigation.
• Small irrigations early
in season.
• 15 cm and 30 cm seem
to be best.

36. Economic Analysis
• Sensitivity to energy prices: Net revenue, not including overhead ($ ha-1):
Irrigation applied
(mm) Yield (t ha-1)
Diesel @
$0.92 liter-1
Diesel @
$1.06 liter-1
Electricity @
$0.025 MJ-1
Baseline 762 15.2 $2,888.69 $2,874.91 $2,950.12
Recommendation 559 15.2 $2,914.41 $2,904.30 $2,959.45
Deficit Irrigation 356 11.1 $1,936.24 $1,929.81 $1,964.90
• Sensitivity to hay prices: Net revenue, not including overhead ($ ha-1):
Irrigation applied
(mm) Yield (t ha-1) $157§ t-1 $242† t-1 $274‡ t-1
Baseline 762 15.2 $1,584.76 $2,888.69 $3,378.50
Recommendation 559 15.2 $1,610.48 $2,914.41 $3,404.22
Deficit Irrigation 356 11.1 $987.05 $1,936.24 $2,292.79
Describe the field

37. Potential $ Savings
• Savings per ha relative to baseline (762 mm applied and yield of 15.2 t ha-1)†:
Energy Price
Diesel @ $0.92 liter-1 Diesel @ $1.06 liter-1 Electricity @ $0.025 MJ-1
Recommendation (559 mm
applied and yields of 15.2 t ha-1) $25.72 $29.39 $9.34
Deficit Irrigation (356 mm
applied and yields of 11.2 t ha-1) -$952.45 -$945.11 -$985.21
†Hay price fixed at $242.07 t-1
• Savings per ha relative to baseline (762 mm applied and yield of 15.2 t ha-1)‡:
Hay Price ($ t-1)
$156.53 t-1 $242.07 t-1 $274.20 t-1
Recommendation (559 mm
applied and yields of 15.2 t ha-1) $25.72 $25.72 $25.72
Deficit Irrigation 356 mm
applied and yields of 11.2 t ha-1) -$597.71 -$952.45 -$1,085.71
‡Energy price fixed at $1.06 liter-1
• Potential savings over the whole field: $460 to $1,500 per year.

38. Conclusions
1. No significant differences found in yield, forage
quality and WUE among varieties.
2. Significant difference between irrigation
treatments for yield and WUE.
3. WUE and quality more affected by the time of
the year than by the irrigation amount.
4. Similar, or better, alfalfa yields can be produced
with less water, with proper irrigation
scheduling.
5. Economic analysis showed large potential
energy savings, ranging from $9 to almost $30
ha-1.

39. Literature Cited
• Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998. Crop evapotranspiration: Guidelines for computing crop water requirements. FAO Irrigation and drainage paper
56. Irrigation and Drainage 300(56):1–15.
• California Alfalfa and Forage Association. 2004. Commodity Fact Sheet Alfalfa. California Foundation for Agriculture in the Classroom, Sacramento, CA.
• Ditterline, R.L., R.L. Dunn, S.D. Cash, D.M. Wichman, L.E. Welty, J.L. Bergman, J.L.A. Eckhoff, M.E. Majerus, J.G. Scheetz, L.K. Holzworth, K.R. Blunt, L.S. Strang, and J.
• North American Alfalfa Improvement Conference. 1999. Mountaineer. Description of Alfalfa Cultivars and Germplasms. Available at
http://www.naaic.org/varietyaps/mountaineer.htm (verified 4 November 2012).
• Oregon Hay and Forage Association. USDA quality guidelines for alfalfa hay . Hay Quality Designations. Available at
http://www.oregonhaygrowers.com/qualitytesting.html (verified 8 May 2013).
• Vavrovsky. 2001. Registration of `Shaw’ Alfalfa. Crop Science 41(1): 264–265Available at https://www.crops.org/publications/cs/articles/41/1/264 (verified 24 January
2012).
• Russelle, M. 2001. After an 8,000-year journey, the“ Queen of Forages” stands poised to enjoy renewed popularity. American Scientist 89: 252.
• USDA NASS. 2012. USDA NASS Quickstats. Available at http://quickstats.nass.usda.gov/ (verified 17 March 2012).
• Walter, I.A., R.G. Allen, R. Elliott, M.E. Jensen, D. Itenfisu, B. Mecham, T.A. Howell, R. Snyder, P. Brown, S. Eching, T. Spofford, M. Hattendorf, R.H. Cuenca, J.L. Wright,
and D. Martin. 2000. ASCE’S Standardized Reference Evapotranspiration Equation. p. 209–215. In National Irrigation Symposium. American Society of Agricultural
Engineers, Phoenix, AZ, USA.

40. THANK YOU!
o Mike Killen and his crew
o UW Agricultural
Experiment Station
o Advisor: Axel Garcia y
Garcia
o Co-advisors: Anowar Islam
& Kristi Hansen
o Joan Tromble and Andrea
Pierson
o My family

41. QUESTIONS?