This study examined differences between targeted and actual irrigation amounts applied to soybean fields in Arkansas. Researchers found that actual water usage exceeded targets by 0.4 to 2.9 acre-inches per treatment. Extrapolated across all irrigated soybean acres in the state, this could mean over 1 billion extra acre-inches of water used, costing an estimated $2.9 million. The costs of applying more water than planned ranged from $1.08 to $7.86 per acre depending on the treatment. This has implications for water conservation and farm budgets in Arkansas soybean production.

1. Economic Differences in Soybean
Production Systems of Budget Estimated
Irrigation Water Use Versus Actual Use
C.Robert Stark
(stark@uamont.edu)
Presented at the Soil & Water Conservation Society
71st International Annual Conference
Louisville, Kentucky, July 24‐27, 20165
Paul Francis
(francis@uamont.edu)
Leo Espinoza
(lespinoza@uaex.edu)
Chris Henry
(cghenry@uark.edu)
Mukhammadzakhra Ismanov
(mismanov@uark.edu)
Larry Earnest
(learnest@uark.edu)
Scott Hayes
(shayes@uark.edu)

2. Soybean in Arkansas
3.11
2.85
3.3
3.42
3.19
3.33
3.2
3.27 3.24
3.3
3.15
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
Total Acres Planted
(MillionAcres)

3. Soybean in Arkansas
1.963
2.18 2.125
2.48 2.565
2.348
2.627 2.53
2.68 2.65 2.71
0.0
0.5
1.0
1.5
2.0
2.5
3.0
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Total Irrigated Acres Planted
(Million Acres)

4. Soybean in Arkansas
39.0 39.0 40.0 41.0 39.0 39.5
42.2
48.3 46.4
52.5 51.4
0.0
10.0
20.0
30.0
40.0
50.0
60.0
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Irrigated Annual Average Yield
(Bushels/Acre)

5. Soybean in Arkansas
34.0 35.0 36.0
30.0
37.5
35.0
38.5
43.5 43.5
50.0 49.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Statewide Annual Average Yield
(Bushels/Acre)

6. Study Questions
1. Are there differences in the
targeted quantities of water per
irrigation event and actual amounts
being applied in soybean irrigation?
2. What are the resource and
economic costs of water quantity
variations in soybean irrigation?

7. Agronomic Research Design
• Soybean Irrigation Studies
– Southeast Research Station, Rohwer, Arkansas, 2015
Data from 2 Studies:
• Sharkey Silty Clay soil – Gypsum‐Ripping‐Deficit Irrigation
• Silt Loam soil – Deficit Irrigation

8. Agronomic Research Design
• Soybean Irrigation Studies
– Randomized Complete Block design with 4 replications.
Treatments were independent of the block design.

9. Agronomic Research Design
• Soybean Irrigation Initiation Study
– Watered from well with 80’ water table, pumped from
approx. 100’, by 3‐stage electric pump (100 acre capacity).
– Irrigation volume was determined using a flowmeter
attached at the well.

10. Agronomic Research Design
• Soybean Irrigation Initiation Study
– Irrigation timing was based on readings from the ETGage™
using the “Alfalfa Cover” setting.

11. Agronomic Research Design
• Soybean Irrigation Initiation Study
– Fertilization was applied according to annual soil tests.
– Management practices followed UA‐CES recommendations
for weed, insect, and disease control.

12. Deficit Irrigation Initiation Treatments
Sharkey Clay Gyp‐Rip‐Def Study:
–2 inch Water Deficit – Applied three
irrigations on June 22, August 3, and August
14.
–3 inch Water Deficit – Applied two
irrigations on July 27 and August 10.
–4 inch Water Deficit ‐ Applied one irrigation
on August 3.

13. Deficit Irrigation Initiation Treatments
Silty Loam Deficit Study:
–1.5 inch Deficit – Applied six irrigations on
June 22, July 15, 21, & 27 and August 5 & 14.
–2.5 inch Deficit – Applied three irrigations on
July 21, August 5, and August 17.
–3.5 inch Deficit – Applied two irrigations on
July 27 and August 17.
–4.5 inch Deficit ‐ Applied two irrigations on
August 3 and August 17.

14. 2.83 2.90
4.66
13.65
5.48
2.90
0
2
4
6
8
10
12
14
6/22/2015 7/27/2015 8/3/2015 8/10/2015 8/14/2015
Actual
Acre‐Inches
Water
Applied
2015 Sharkey Clay Gyp‐Rip‐Def Study
2 inch deficit 3 inch deficit 4 inch deficit
2.5” Target
Acre‐Inches
Per
Treatment

15. 2.74
7.80
3.47
2.80
1.93
2.37
5.91
3.04
0
1
2
3
4
5
6
7
8
6/22 7/15 7/21 7/27 8/3 8/5 8/14 8/17
Actual
Acre‐Inches
Water
Applied
2015 Silt Loam Deficit Irrigation Study
1.5 inch deficit 2.5 inch deficit
3.5 inch deficit 4.5 inch deficit
2.5” Target
Acre‐Inches
Per
Treatment

16. Actual Irrigation Variability‐Sharkey
DATE CHANGE FROM
TARGET (acre‐inches)
June 22 + 0.33
June 27 X
August 3 + 0.80
August 10 + 2.98
August 14 + 2.16
+ 6.27

17. Actual Irrigation Variability‐Silt
DATE CHANGE FROM TARGET (acre‐inches)
June 22 + 0.24
July 15 X
July 21 + 1.94
July 27 + 0.60
August 3 + 3.41
August 5 ‐ 1.14
August 14 ‐ 0.13
August 17 + 1.62
+ 6.54

18. Actual Variability by Treatment‐Sharkey
TREATMENT # Target
Volume
Actual
Volume
2.0” Deficit 3 7.5” 10.39
3.0” Deficit 2 5.0” 19.13 ?
4.0” Deficit 1 2.5” 2.90

19. Actual Variability by Treatment‐Silt
TREATMENT # Target
Volume
Actual
Volume
1.5” Deficit 6 15.0” 21.11 ?
2.5” Deficit 3 7.5” 8.44
3.5” Deficit 2 5.0” 5.84
4.5” Deficit 2 5.0” 8.95 ?

20. • Partial Budget approach used 2015 UA Division of
Agriculture interactive enterprise budgets.
• Irrigation quantity cost comparisons were developed
by calculating costs for target quantities per treatment
and then adjusted to reflect actual quantities applied.
Economic Research Methods

21. • Inputs by year were actual products
& quantities.
• Input prices per unit were taken from
UA Division of Agriculture &
Mississippi State Budget Generator
2015 lists.
Economic Research Methods

22. Actual Cost Change by Treatment‐Sharkey
TREATMENT # Target
Volume
Actual
Volume
Change
in Cost
2.0” Deficit 3 7.5” 10.39 +$ 7.86
3.0” Deficit 2 5.0” 19.13 ? +$ 38.43
4.0” Deficit 1 2.5” 2.90 +$ 1.08

23. Actual Variability by Treatment‐Silt
TREATMENT # Target
Volume
Actual
Volume
Change
in Cost
1.5” Deficit 6 15.0” 21.11 ? +$ 16.61
2.5” Deficit 3 7.5” 8.44 +$ 2.56
3.5” Deficit 2 5.0” 5.84 +$ 2.29
4.5” Deficit 2 5.0” 8.95 ? +$ 10.74

24. Actual Water Usage Differences

25. Actual Water Usage Differences

26. Conclusions
1. Differences exist between target volumes for
irrigation treatments and actual volumes ranging
from 0.40 acre‐inches to 2.89 acre‐inches.
2. Extended across all 2015 irrigated soybean acres
planted in Arkansas, added use could exceed 1.084
million acre‐inches or 29.484 billion gallons.
3. Operating and Capital Recovery Costs associated with
extra irrigation water use ranged from $1.08 per acre
to $7.86 per acre.
4. Extended on average across all 2015 irrigated soybean
acreage harvested in Arkansas, the added total
expense could exceed $2.9 million.

27. Acknowledgments
 Arkansas Soybean
Promotion Board.
 Dr. Kelly Bryant, Dean UAM School of Agriculture
Director, UA Southeast Research & Extension Center
Monticello, AR.
 Research Station Director and Staff
Southeast Research Station, Rohwer, AR.

28. Questions??