This document discusses deficit irrigation techniques for row crops in humid regions. It describes how managed depletion irrigation (MDI) can provide drought mitigation, environmental protection, and optimized crop yields. Small plot studies on soybeans and cotton were conducted to determine optimal MDI levels and timings. A new irrigation scheduling tool called MOIST+ was developed that incorporates recommendations from the yield studies and uses soil matric potential sensors and a water balance model to provide deficit irrigation recommendations. The tool and techniques were demonstrated on producer fields.

1. Deficit Irrigation of Row Crops Provides Drought
Mitigation, Environmental Protection, and
Optimized Yield in Humid Regions
Dr. Brian Leib, Extension Irrigation Specialist
Tim Grant, Irrigation Extension Assistant
Biosystems Engineering & Soil Science, University of Tennessee
USDA-NRCS Conservation Innovation Grant Showcase
at the 73rd Annual Conference of the Soil and Water Conservation Society
Albuquerque, NM -- July 29 to August 1, 2018
Also supported by Cotton Inc., Tennessee Soybean Promotion Board,
and the Southern Soybean Research Project

2. “Deficit”, “Reasonable Depletion” or “Managed Depletion” Irrigation
to Optimize Center Pivot Irrigation in a Humid Region
• 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
-300
-250
-200
-150
-100
-50
0
7/2 7/12 7/22 8/1 8/11 8/21 8/31
SoilMatricPotential(kPa)
~Full
6"
18"
-300
-250
-200
-150
-100
-50
0
7/2 7/12 7/22 8/1 8/11 8/21 8/31SoilMatricPotential(kPa)
Deficit
6"
18"

3. • Develop an Irrigation Scheduling Tool based on the
needs of a Humid Region.
• Help Interpret Results from a New Type of Soil
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 the Water Balance by
Connecting a Rain Gauge to the Data Logger.
• Record Irrigation Amount and Water Management
Practices to Validate Cost-Share Programs and
Measure Withdrawal from Water Sources.
METER Logging System
with MPS-2 Sensor
MOIST+ (Management Of Irrigation Plus Soil Tension)
Why Develop a New Irrigation Scheduling Tool?

4. Matric Potential Sensors Compared
in a Pressure Plate Experiment
-300
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-200
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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
WaterMark
MPS-2 & MPS-6

5. Soybean Small Plot Trials to Determine
Managed Depletion Irrigation (MDI) Levels

6. Soybean Yield Results from MDI Trials

7. -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"
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-400
-300
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-100
0
11-Jun 3-Jul 25-Jul 16-Aug 7-Sep
SoilMoisture
R3 1.0"/wk
103 6"
103 18"
-500
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-200
-100
0
11-Jun 3-Jul 25-Jul 16-Aug 7-Sep
SoilMoisture
Dryland
108 6"
108 18"
Soil Matric Potential Results from
the 2016 MDI Trials in Soybean

8. Cotton Small Plot Trials in Variable Soils to Determine
Managed Depletion Irrigation (MDI) Levels

9. Cotton Yield Results from MDI Trials
Sandy Silt Loam over Sand Deep Silt Loam
Rainfed
Yield
(lbs/ac)
Deficit
Irrigated
Yield
(lbs/ac)
Optimal
Treatment
(Stage,
Rate)
Irrigation
Applied
(in)
Rainfed
Yield
(lbs/ac)
Deficit
Irrigated
Yield
(lbs/ac)
Optimal
Treatment
(Stage,
Rate)
Irrigation
Applied
(in)
Rainfed
Yield
(lbs/ac)
Deficit
Irrigated
Yield
(lbs/ac)
Optimal
Treatment
(Stage,
Rate)
Irrigation
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

10. Cotton Small Plot MDI Trials
Effect of soil and irrigation on N uptake

11. MOIST+ Spreadsheet with Meter Group (Decagon)
Equipment Demonstrated in Producer Fields
Rainfall
&
Irrigation
Temperature
&
Humidity
Soil
Matric
Potential
Solar
Radiation
Logger to Cell Phone to
Internet

12. Examples of the MOIST+ Spreadsheet

13. Cross Platform MOIST+ APP is being developed with
MDI Recommendations Incorporated
Farm: B.E. Smith Field: Back 40 Zone: Side Slope
Crop: Soybean
Variety: AP 6111
Growth Stage: R5
1 2 3 YTD
ET 0.18 0.20 0.17 12.0
Rain 1.0 0.0 0.0 8.0
Irrig 0.0 0.0 0.5 2.0
Days Past
SoilTension
SeasonGraph
Button
WaterBalance
SeasonGraph
Button
Date: 07/28/2018
Logger: 07/28/2018
RootGrowth
1. Record of Irrigation
Water Management for
Cost-Share Validation.
2. Measured record of
Irrigation for Management
of Water Resources.
3. How should Irrigation
Management Tools be
adapted to better serve
other regions?