How to maximize yields with the least amount of water Replacing crop water use to a full point or field capacity is a common approach to irrigation scheduling. At least, that’s true in arid climates. But what if there’s a repeat chance of rain? Uncertainty of rainfall amount and timing can impact how we approach irrigation water management. ​In humid regions​, bringing the soil to full field capacity often means lost yield potential. Brian Leib, Ph.D., from the University of Tennessee presents this webinar presentation to discuss a new approach to managing irrigation. He’ll share past studies and results using different irrigation treatments in soybean and cotton crops. Learn how to: • Manage for rainfall in humid regions • Avoid issues with runoff to low, poorly drained areas • Promote reproductive growth and root development • Adapt principles from arid climates

2. MANAGED DEPLETION
IRRIGATION (MDI)
FOR HUMID REGIONS AND BEYOND
Brian Leib, PhD
Biosystems Engineering & Soil Science
University of Tennessee

3. “DEFICIT,” “REASONABLE
DEPLETION,” OR “MANAGED
DEPLETION” IRRIGATION
3
• Deficit vs. full irrigation
(rainfall + irrigation) < crop water use
• Better conditions for rainfall capture
• Prevent excess soil water where there is
potential for poor drainage
• Less water on canopy
• Promote reproductive instead of
vegetative growth

4. 4
-300
-250
-200
-150
-100
-50
0
7/2 7/12 7/22 8/1 8/11 8/21 8/31
SoilMatricPotential(kPa)
Full Irrigation sometimes with Reduced Yield
6"
18"
-300
-250
-200
-150
-100
-50
0
7/2 7/12 7/22 8/1 8/11 8/21 8/31
SoilMatricPotential(kPa)
Managed Deficit with Full Yield
6"
18"
DEFICIT VS FULL IRRIGATION

5. MDI IN THE SOIL WATER
CONTINUUM
5
ManagedDepletionIrrigation
FullIrrigation
AvailableSoilWaterHoldingCapacity
SATURATION
MINERAL SOIL
OVEN DRY
WILTING POINT
MAD
FIELD CAPACITY
MINERAL SOIL
OVEN DRY
WILTING POINT
MAD
FIELD CAPACITY
MINERAL SOIL
OVEN DRY
WILTING POINT
MAD
MINERAL SOIL
OVEN DRY
WILTING POINT
Too Wet for Most Plants
Water Lost by Drainage
Leaching of Ag Chemicals
Water Stored by Pores
Easily Available to Plants
Plants Access Water
Under Stress
Plant Mortality
AIR
AIR
AIR
3.0”
1.0”
1.0”
0.5”
6.5”

6. WATER BALANCE EXAMPLE
MDI FOR CENTER PIVOT
6
0.3 to 0.5 inches per revolution on
> 2% slopes recommended
Full Irrigation
Day 1 Day 2 Day 3 Day 4 Day 5
ET 0.25 0.25 0.25 0.25 0.25
Rain 0.0 0.0 0.0 0.0 2.0
Irrigation 0.5 0.5
Soil Depletion 0.25 0.0 0.25 0.0 -1.75
Managed Depletion Irrigation
Day 1 Day 2 Day 3 Day 4 Day 5
ET 0.25 0.25 0.25 0.25 0.25
Rain 0.0 0.0 0.0 0.0 2.0
Irrigation 0.5 0.5
Soil Depletion 1.75 1.5 1.75 1.5 -0.25

7. WHY MATRIC POTENTIAL?
VS VOLUMETRIC WATER CONTENT
7

8. SOIL SENSOR READINGS
ON 09/01/1999 IN WSU ALFALFA
8
• EnviroSCAN 4.31 in/ft
• TDR 4.17 in/ft
• Trime 3.53 in/ft
• AquaTel 3.08 in/ft
• Troxler RF 3.08 in/ft
• Neutron Probe 2.90 in/ft
• Tensiometer 2.51 in/ft
• WaterMark 2.45 in/ft

9. 9
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
4/20 5/21 6/21 7/22 8/22 9/22
in/ft
WSU ALFALFA 1999 WEST 12 inch
Neutron Probe Neutron Probe r Tensiometer Trime Troxler Watermark Watermark m Enviroscan Aqua-Tel TDR

10. 0
1
2
3
4
5
6
Sand Sandy Loam Loam Silt Loam Clay Loam
SoilWaterContent(in/ft)
Field Capacity
Wilting Point
10
SOIL TEXTURE VS WATER
HOLDING PROPERTIES

11. COMPARISON STUDY
MATRIC POTENTIAL SENSORS
8/28/19 11
Tensiometers WaterMark Sensors by
Irrometer
MPS-2 & MPS-6/TEROS
21 by METER
Granular matrix with
electrical capacitance
Granular matrix with
electrical resistance
Direct measurement of
soil tension

12. PRESSURE CHAMBER
EXPERIMENT
8/29/19 12
3 Used Matric Potential Sensors
• WaterMark, MPS-2, MPS-6/TEROS 21
2 Runs of 0 to 300 kPa
• Silt loam soil
• Loamy sand soil
Comparison
• True matric potential
• Sensor types
• Soils of different water holding capacity

13. 13
-300
-250
-200
-150
-100
-50
0
-300-250-200-150-100-500
Sensor(kPa)
Pressure Plate (kPa)
Comparison of Matric Potential Sensors (full range)
Silt-WM Silt-MPS2 Silt-MPS6
Sand-WM Sand-MPS2 Sand-MPS6
1 to 1

14. CREATING MANAGED DEFICITS
BY IRRIGATION TIMING AND AMOUNT IN
COTTON (2006 TO 2014)
8/28/19 14
1.5” per week
1.0” per week
0.5” per week
1. First Square
2. First Bloom
3. Post Bloom

15. 15
2006-2009 YIELD RESULTS
IN A DEEP SILT LOAM SOIL
Year Variety Growing
Season Rain
Optimum
Irrigation
Total
Water
Optimum
Irrigation
Treatment
Optimum
Irrigation
Yield
Rainfed
Yield
Yield
Increase
in in in lbs/ac lbs/ac lbs/ac
2006 DP 143 17.3 2.6 19.9 FS 0.5/wk 1867 1566 301
2007 DP 143 11.6 6.7 18.3 PB 1.5/wk 1850 923 927
2008 PHY 375 15.0 3.6 18.6 FB 1.0/wk 2294 1866 428
2009 PHY 375 21.3 0.0 21.3 none none 1112 0

16. COTTON YIELD RESULTS
IN MIXED SOILS
8/28/19 16
Sandy Silt Loam over Sand Deep Silt Loam
Rainfed
Yield
(lbs/ac)
Deficit
Irrigate
d Yield
(lbs/ac)
Optimal
Treatme
nt
(Stage,
Rate)
Irrigatio
n
Applied
(in)
Rainfed
Yield
(lbs/ac)
Deficit
Irrigate
d Yield
(lbs/ac)
Optimal
Treatme
nt
(Stage,
Rate)
Irrigatio
n
Applied
(in)
Rainfed
Yield
(lbs/ac)
Deficit
Irrigate
d Yield
(lbs/ac)
Optimal
Treatme
nt
(Stage,
Rate)
Irrigatio
n
Applied
(in)
2010
(wet)
519 1062 Bloom
1.5
7.2 789 1447 Bloom
0.5
2.4 1336 1336 Rainfed 0
2011
(late dry)
405 1486 Square
1.5
8.2 900 1374 Bloom
0.5
2.2 1385 1668 Bloom
0.5
2.2
2012
(early dry)
425 1374 Square
1.5
8.5 872 1615 Square
1.0
5.7 1108 1522 Square
1.0
5.7
2013
(wet)
1028 1744 Bloom
1.5
3.6 1242 1836 Bloom
1.5
3.6 1705 1705 Rainfed 0
2014
(wet)
149 1464 Sq 0.5,
Bl 1.5
6.3 1219 1396 Bloom
1.0
3.8 1452 1452 Rainfed 0
Average 505 1426 6.8 1004 1534 3.5 1397 1537 1.6

17. IRRIGATION OF COTTON
IN MIXED SOILS
WTREC IN JACKSON, TN (2010 TO 2012)
8/28/19 17
0
200
400
600
800
1000
1200
1400
1600
0" 4" 8"
Yield(lbs/ac)
Irrigation
Silt Loam
Sand

18. CREATING MANAGED DEFICITS
BY IRRIGATION TIMING AND AMOUNT IN
SOYBEAN (2013 TO 2018)
8/28/19 18

19. SUMMARY
PAST SOYBEAN IRRIGATION RESULTS
DEEP SILT LOAM SOIL (JACKSON, TN)
8/29/19 19
10 Soybean Irrigation Treatments
Initiate at R1 0.5”/wk 1.0”/wk 1.5”/wk
Initiate at R3 0.5”/wk 1.0”/wk 1.5”/wk
Initiate at R5 0.5”/wk 1.0”/wk 1.5”/wk
Rainfed Adjusted irrigation by rainfall
Year Rain (in) Irrigation (in) Best Timing &
Amount
Best Irrigated
Yield (bu/ac)
Rainfed Yield
(bu/ac)
Yield Increase
(bu/ac)
2013 - 2016 22.8 1.8 R5 - 1.0”/wk > 80 70 10
2017 21.8 4.7 R3 – 1.5”/wk 51 40 11

20. MATRIC POTENTIAL RESULTS
2016 MDI SOYBEAN TRIALS
8/28/19 20
-500
-400
-300
-200
-100
0
11-Jun 3-Jul 25-Jul 16-Aug 7-Sep
SoilMoisture
R5 1.0"/wk
102 6"
102 18"
-500
-400
-300
-200
-100
0
11-Jun 3-Jul 25-Jul 16-Aug 7-Sep
SoilMoisture
R1 1.5"/wk
107 6"
107 18"
-500
-400
-300
-200
-100
0
11-Jun 3-Jul 25-Jul 16-Aug 7-Sep
SoilMoisture
R3 1.0"/wk
103 6"
103 18"
-500
-400
-300
-200
-100
0
11-Jun 3-Jul 25-Jul 16-Aug 7-Sep
SoilMoisture
Dryland
108 6"
108 18"

21. 2018 EXPERIMENT
IN SOILS THAT VARY IN WATER HOLDING
CAPACITY
8/29/19 21
7 Soybean Irrigation Treatments
Initiate at R1 1.1”/wk 1.6”/wk
Initiate at R3 1.1”/wk 1.6”/wk
Initiate at R5 1.1”/wk 1.6”/wk
Rainfed Adjusted irrigation by rainfall
Sandy Silt over
Sand
Deep Silt
AWHC 0.7 in/ft 1.4 in/ft 2.1 in/ft
Treatment 7 7 7
Reps 4 3 4
Plots 28 21 28

22. 8/28/19 22
24” RAIN IN GROWING SEASON
MAY 24 – SEPTEMBER 12
VISUAL STRESS

23. YIELD RESULTS
2018 SOYBEAN IRRIGATION IN MIXED SOIL
JACKSON, TN
8/28/19 23

24. 8/28/19 24
-500
-400
-300
-200
-100
0
30-May 6-Jun 13-Jun 20-Jun 27-Jun 4-Jul 11-Jul 18-Jul 25-Jul 1-Aug 8-Aug 15-Aug 22-Aug 29-Aug
SoilMatricPotential(kPa)
Soil Matric Potential in Highest Rate and Earliest Irrigated Sandy Plot
6" - R1 HI 24" - R1 HI
IDENTIFYING
IRRIGATION TRIGGER POINTS

25. 8/28/19 25
-500
-400
-300
-200
-100
0
30-May 6-Jun 13-Jun 20-Jun 27-Jun 4-Jul 11-Jul 18-Jul 25-Jul 1-Aug 8-Aug 15-Aug 22-Aug 29-Aug
SoilMatricPotential(kPa)
Soil Matric Potential in Lowest Rate and Latest Irrigated Silt Loam Plot
6" - R5 LOW 24" - R5 LOW
IDENTIFYING
IRRIGATION TRIGGER POINTS

28. MOIST+
(MANAGEMENT OF IRRIGATION PLUS SOIL
TENSION) Why develop a new irrigation scheduling
tool?
• Address needs of humid regions
• Help interpret results from a new type of
matric potential sensor
• Incorporate recommendations from yield
studies designed to identify MDI levels
• Use a water balance and soil sensor approach
simultaneously
• Automate inputs to water balance with rain
gauge
• Record irrigation amount and water
management practices 28
METER
Logging
System
with MPS-2
Sensor

29. FARMER ADVICE
29
“Don’t get knocked out by
any fat bean pods.”

30. MOIST+ WATER BALANCE
30

31. MOIST+ WEB APP
DEMONSTRATION
31
+

32. MDI AND MOIST+ APPROACH
OTHER APPLICATIONS
6”
8”
12”
18-24”
30-36”
Partial root-zone drying Subsurface drip Furrow

33. QUESTIONS?
Brian Leib, PhD
Biosystems Engineering & Soil Science
University of Tennessee
QUESTIONS?
Brian Leib, PhD
Biosystems Engineering & Soil Science
University of Tennessee