Pecan Irrigation

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Pecan Irrigation
Michael Kizer OSU Extension Irrigation Specialist
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Irrigation Water Management

• Good irrigation water management is efficiently
  supplying the proper amount of water to a crop at
  the proper time so that optimum production
  results with minimum expense.

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Irrigation Application Depth(the proper amount)

• Crop rooting depth
• Soil water holding capacity
• Allowable water deficit

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Pecan Root System

• Effective Rooting Depth 4 - 6 feet
• Majority of root volume in upper 2 feet
• Local features (bedrock, etc) may limit depth
• Spread horizontally until competition is met
• Root growth affected by
• irrigation depth
• irrigation frequency
• application pattern

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Soil Water Holding Capacity
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Maximum Allowable Deficit

• Depleting soil water in the pecan root zone by
  more than 50 can lead to
• slowed tree growth
• reduced nut yield
• blanking abortion

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Example 1

• Pecan effective root depth 4 feet
• Durant loam 2.2 in/ft
• Max. Allowable Deficit 50 depletion
• 4 ft x 2.2 in/ft x 50/100 4.4 in
• The trees can remove 5.5 inches of water from
  this soil before they become seriously stressed
  for moisture.

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Example 2

• Pecan effective root depth 4 feet
• Eufala fine sand 0.8 in/ft
• Max. Allowable Deficit 50 depletion
• 4 ft x 0.8 in/ft x 50/100 1.6 in
• The trees can remove 1.6 inches of water from
  this soil before they become seriously stressed
  for moisture.

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Irrigation Interval(the proper time)

• How long will it take to deplete 1.6 inches of
  soil water?
• It depends on the evapotranspiration (ET) rate.

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Evapotranspiration Rate

• Weather conditions - Solar radiation -
  Air temperature - Wind speed -
  Relative humidity
• Cultural Practices - Nutritional
  management - Pest stresses - Irrigation
  amount frequency

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Irrigation Interval(the proper time)

• How long will it take to deplete 1.6 inches of
  soil water?
• At ET0.31 in/day it will take about 5 days.

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Mesonet Ag. Weather Page

• http//agweather.mesonet.org

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Tensiometer for measuring soil water potential
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Electrical resistance blocks w/ meters
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Irrigation Water QualitySalinity

• Pecans are moderately sensitive to salinity
• Threshold ECe for yield reduction 1.9
  dS/m (1900 ?mho/cm)
• Yield reduction rate 16 / added dS/m
• 50 yield reduction _at_ ECe 4.9 dS/m
  Note (1dS/m 1 mmho/cm 1000 ?mho/cm)

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Irrigation Water QualityBoron

• Pecans are very sensitive to boron
• Threshold soil boron concentration for onset of
  yield reduction 1.0 mg/L

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Irrigation Water Testing Before you go very
far in an irrigation development plan, get an
irrigation water test for 15 from the OSU Soil,
Water Forage Analytical Lab. through your
County Extension Educator
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Irrigation System Options

• Flood irrigation
• Sprinkler irrigation -Solid set
  sprinklers -Traveling volume gun
• Microirrigation

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Flood Irrigation

• Furrow systems
• Low initial cost (in most cases)
• Low pressure/energy requirement
• Low application efficiency

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Rainbird 30, 14 and 65 impact sprinkler heads
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Typical solid set sprinkler field layout
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Solid Set Sprinklers

• Irrigate trees and cover crop
• Low labor requirement
• Moderate pressure/energy requirement
• Moderately efficient application (70-80)
• Non-portable (permanent system)
• Limits orchard access (temporary system)

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Turbine-driven hard-hose traveling gun sprinkler
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Typical traveling volume gun field layout
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Traveling Gun Sprinklers

• Portable
• Adaptable to irregularly shaped fields
• Irrigates both trees and cover crop
• High pressure (120 psi at hose inlet)
• Lower application efficiency (60-70)
• Less suitable as trees mature

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Micro-sprinklers w/ spinner and fixed diffusers
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Micro-sprinkler w/ fixed, grooved diffuser plate
on a stake w/supply tube
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On-line, button-type drip emitters
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Single multi-outlet, pressure-compensating
emitters on PE tubing
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Drip tape w/ turbulent flow emitter manufactured
in tube seam (T-Tape)
Drip tape w/ PVC emitter welded in seamless PE
tube (Netafim Typhoon)
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Pre-set Pressure Regulators for Microirrigation
Note 2.31 ft of elevation increase 1 psi in
pressure decrease 2.31 ft of
elevation decrease 1 psi in pressure increase
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Zone 2
Zone 1
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Microirrigation system with multi-emitter
pigtail around tree
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Microirrigation Systems

• Highly efficient application (90)
• Low pressure/energy requirement
• Low operating labor requirement
• High initial cost
• Non-portable system
• Best suited to irrigate trees only
• Clean water required (filtration)

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Backflow Prevention

• Protects water source from contamination by
  non-potable water in case of unexpected pressure
  loss in the system. Required by federal law on
  irrigation systems which apply fertilizer and
  pesticides.

• Gooseneck pipe loop with Pressure Vacuum Breaker
• Reduced Pressure Zone device (RPZ)
• Double check valve (Not approved for public
  water systems)

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2 ft min. above highest outlet
Gooseneck pipe loop w/ PVB backflow preventer
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Reduced Pressure Zone (RPZ) Backflow Preventer
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Good Irrigation Management

• Know your soil
• water holding capacity
• infiltration rate
• Know your crop
• rooting depth
• max. allowable deficit
• Know your soil water status or ET rate
• Know your irrigation system
• application rate

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Good Irrigation Management

• Saves water
• Reduces nutrient and pesticide leaching
• Improves quality productivity of the crop
• Saves You Money

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http//biosystems.okstate.edu/Home/mkizer/index.ht
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The End