Pecan Irrigation Michael Kizer OSU Extension Irrigation Specialist
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.
Irrigation Application Depth(the proper amount) • Crop rooting depth • Soil water holding capacity • Allowable water deficit
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
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
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.
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 1.6inches of water from this soil before they become seriously stressed for moisture.
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.
Evapotranspiration Rate • Weather conditions:- Solar radiation - Air temperature - Wind speed - Relative humidity • Cultural Practices:- Nutritional management - Pest stresses - Irrigation amount & frequency
Irrigation Interval(the proper time) How long will it take to deplete 1.6 inches of soil water? At ET=0.31 in/day it will take about 5 days.
Mesonet Ag. Weather Page http://agweather.mesonet.org
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 @ECe = 4.9 dS/mNote: (1dS/m = 1 mmho/cm= 1000 mho/cm)
Irrigation Water QualityBoron • Pecans are very sensitive to boron • Threshold soil boron concentration for onset of yield reduction: ~1.0 mg/L
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
Irrigation System Options • Flood irrigation • Sprinkler irrigation -Solid set sprinklers -Traveling volume gun • Microirrigation
Flood Irrigation • Furrow systems • Low initial cost (in most cases) • Low pressure/energy requirement • Low application efficiency
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)
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
Drip tape w/ turbulent flow emitter manufactured in tube seam (T-Tape) Drip tape w/ PVC emitter welded in seamless PE tube (Netafim Typhoon)
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
Zone #2 Zone #1
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)
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)
2 ft min. above highest outlet Gooseneck pipe loop w/ PVB backflow preventer
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
Good Irrigation Management • Saves water • Reduces nutrient and pesticide leaching • Improves quality & productivity of the crop • Saves You Money