Oct 2001 Methods to Monitor Soil Water Status, Schedule Irrigation Michael van Bavel Dynamax Inc. Houston TX

Oct 2001 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

Oct 2001 Transpiration (T) - Sap flow - Water status T T = K (Ps- P L ) PLPL PSPS Sap Flow (Ps- P L ) T K = Hydraulic Conductivity, Cohesion Tension Theory

Oct 2001 Soil and plant water status factors 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

Oct 2001 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

Oct 2001 Soil Moisture Water Status -15 Bar 0 Bar -.5 to -3 Bar

Oct 2001 Soil Moisture Methods

Oct 2001 Comparison of sensors for soil water tension -matric potential

Oct 2001 New sensors - soil water content

Oct 2001 Moisture Ranges vs Sensor Accuracy Stress Level < 7% Irrigation Start (7%) Stress Level < 33% Deficit Irrigated Clay B.D g/cm3 Sand B.D. = 1.50 g/cm3 0% 10% 30 % 40 % 50% Field Capacity (10%) WIlting Point 4% Over Irrigated Optimum Growth Moisture Range Optimum Moisture Range Wilting Point 22% Dead Plants - No Production Wasted Water & Fertilizer Irrigation Start Point (33%) Field Capacity (45%) Over Irrigated 20% 60% ML2 RESOLUTION - 1% Wasted Water

Oct 2001 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

Oct 2001 Theta Probe Moisture Display HH2 Moisture Meter: Displays calibrated soil moisture readings in: volumetric soil moisture content (% Vol) water deficit (mm) soil moisture content (m 3.m -3 ) Factory calibrated for organic and mineral millivolts (mV) Logging Memory 1000 readings

Oct 2001 Advanced Portable Moisture Probe Advanced Portable Moisture Probe TH 2 O 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

Oct 2001 FEATURES: Volumetric soil moisture content (% Vol) Soil moisture content (m 3.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

Oct 2001 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

Oct 2001 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.

Oct 2001 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.

Oct 2001 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..

Oct 2001 Selection Criteria - Soil Monitoring 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