Methods to Monitor Soil Water Status, Schedule Irrigation Michael van Bavel Dynamax Inc. Houston TX. Irrigation Scheduling Benefits. Improved production Higher quality fruit Lower fruit pH, greater color intensity Controls vegetative growth Some cases - no difference in Yields
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Methods to Monitor Soil Water Status, Schedule IrrigationMichael van BavelDynamax Inc.Houston TX
Irrigation Scheduling Benefits • Improved production • Higher quality fruit • Lower fruit pH, greater color intensity • Controls vegetative growth • Some cases - no difference in Yields • Water conservation • Reduced nutrient leaching
Transpiration (T) - Sap flow - Water status T = K (Ps- PL) T PL Sap Flow T PS (Ps- PL) K = Hydraulic Conductivity, Cohesion Tension Theory
What affects soil water pressure (- tension)? Soil Water Content Soil type Porosity Organic matter Soil amendments Compaction What affects leaf water pressure (- potential)? Light Temp - R.H. - Wind Leaf conductivity Root conductivity Stem conductivity Plant vigor Soil Water Status Soil and plant water status factors
Monitoring Stress & P at the Leaf • Leaf water potential: • Pressure bomb • - pressure up to 300 psi (20 B) • - force water out of cut leaves • Leaf hygrometer • - Wet bulb vs ambient temp- converted to water potential • Both systems labor and technique intensive • Gives good results - recent press • Not for remote monitoring
Soil Moisture Water Status 0 Bar -.5 to -3 Bar -15 Bar
Moisture Ranges vs Sensor Accuracy Clay B.D. 1.20 g/cm3 Sand B.D. = 1.50 g/cm3 60% Wasted Water Over Irrigated Over Irrigated 50% Field Capacity (45%) Optimum Growth Moisture Range Wasted Water & Fertilizer 40% Irrigation Start Point (33%) Stress Level < 33% Deficit Irrigated 30% 20% Wilting Point 22% Dead Plants - No Production Field Capacity (10%) Optimum Moisture Range 10% Irrigation Start (7%) Stress Level < 7% 0% WIlting Point 4% ML2 RESOLUTION - 1%
Theta Probe Moisture Level Control • ML2 Theta Probe: • no maintenance • buriable to 15 ft depth • unaffected by salinity • permanently sealed, indefinite lifespan • +/- 1% accuracy • volumetric soil moisture content • 0 – 60% range
Theta Probe Moisture Display • HH2 Moisture Meter: Displays calibrated soil moisture readings in: • volumetric soil moisture content (% Vol) • water deficit (mm) • soil moisture content (m3 .m-3) • Factory calibrated for organic and mineral • millivolts (mV) • Logging Memory 1000 readings
Advanced Portable Moisture ProbeTH2O • Features • New technology for measuring soil moisture • Sealed, waterproof probe, factory calibrated • Unaffected by salinity or temp. • Minimal soil disturbance • Benefits • Simple operation - anyone can use it to take readings • Precise moisture readings - • no more guess work • Troubleshooting tool to identify soil moisture problems causing poor turf • Irrigation uniformity monitor - irrigation audit • Stores a complete record of water status • Field water status to 2 ft in access holes
NEW - PR1 Profile Moisture Probe • FEATURES: • Volumetric soil moisture content • (% Vol) • Soil moisture content (m3 .m-3) • Factory calibrated for organic and mineral soils • Easy access tube installation • Sealed, portable probe • 1 m - PR1/6 or 1/2 m PR1/4 models • Typical 5 % accuracy, greater accuracy with soil specific calibration
NEW - PR1 Profile Moisture Probe • FEATURES: • Access tubes inserted at many observation points. • PR1/6 - Reads depth (mm) • 100,200,300,400,600,1000 • PR1/4 - Reads depth (mm) • 100,200,300,400 • HH2 - Hand held reader, displays and stores readings • Complete installation kits available
Advanced Moisture Level Control Example - TMLC • How does it work? • Determine site specific field capacity by taking soil moisture level readings after a saturating rain. • Set desired Irrigation Start Point (% Vol) • The output relay will trigger when irrigation is needed.
TMLC Irrigation System Applications • Satellite and Standard Timer Scheduling: • TMLC controls the power for all valves grouped together. • The ML2 is buried in most critical zone. Valves are enabled when the moisture is below your irrigation start point.
TMLC Irrigation System Applications • Moisture Alarm: • TMLC is an irrigation alarm for field crops. A circuit option allows 12 V DC operation, with a 12 V strobe-alarm light as the indicator..
Will the method measure what you need to know? Who on your staff can use these tools easily? Will the added expense pay for itself? 1% - 3 % precision needed for critical soils - new sensor ML2. No subjective or calibration issues. Irrigation system $5K - $7 K /ac cost? Allocate 5% for water management tools Pays for itself in 1 year - 25% water savings typical Selection Criteria - Soil Monitoring