Irrometer LT Long Tensiometer

Overview

The Irrometer LT (Long Tensiometer) is a professional-grade instrument designed for monitoring soil water tension at deep root zone depths of 36-48 inches (90-120 cm). This long-range model is essential for tracking deep water storage, monitoring drainage and deep percolation, ensuring complete root zone wetting in orchards and vineyards, and preventing water waste through over-irrigation.

Key Features

• Deep Zone Monitoring: Measures soil moisture at 36-48 inch (90-120 cm) depths
• Direct Measurement: Measures actual soil water tension experienced by deep roots
• Drainage Detection: Identifies over-irrigation and deep percolation losses
• Fast Response: Rapid equilibration with soil moisture changes
• Easy Reading: Clear vacuum gauge with centibar scale
• Proven Technology: Time-tested design used worldwide since 1951
• No Calibration: Works in all soil types without calibration
• Professional Grade: Durable construction for long-term field use

Applications

• Deep-rooted orchard crops (citrus, stone fruit, pome fruit)
• Mature vineyard irrigation management
• Deep percolation monitoring
• Drainage assessment
• Complete profile irrigation verification
• Water storage zone monitoring
• Over-irrigation detection
• Preventing groundwater contamination
• Agricultural research
• Water balance studies
• Multi-depth soil moisture profiling

Technical Specifications

The Irrometer LT tensiometer features an extended-length water-filled tube with a porous ceramic cup positioned at the deep measurement depth. Water exchanges through the ceramic cup in response to soil moisture conditions at that depth, creating a vacuum measured by the gauge at the surface. The reading indicates soil water tension where deep roots access water and where excess irrigation causes drainage losses.

Understanding Deep Zone Monitoring

The deep root zone and drainage zone serve critical functions:

Deep Root Water Access

• Drought reserve: Water available during extended dry periods
• Mature plant roots: Established trees and vines access deep water
• Deep watering verification: Confirms irrigation reaches entire root zone
• Root zone extent: Indicates active root zone depth

Drainage and Water Loss Detection

• Over-irrigation indicator: Shows when excess water percolates below roots
• Water efficiency: Identifies wasted irrigation water
• Nitrate leaching: Deep percolation carries nutrients below root zone
• Environmental protection: Prevents groundwater contamination
• Cost savings: Reduces wasted water, energy, and nutrients

Tensiometer Reading Interpretation

Deep Zone Moisture Status

• 0-10 cb: Recent deep percolation, possible over-irrigation
• 10-30 cb: Deep zone well-watered, full profile wetting achieved
• 30-50 cb: Adequate deep moisture reserve
• 50-70 cb: Deep reserve depleting, ensure adequate irrigation depth
• 70-80 cb: Deep zone dry, roots may be stressed if shallow zones also dry

Multi-Depth Comparison Patterns

Pattern 1: Shallow and mid wet, deep dry

• Irrigation not penetrating deep enough
• Increase irrigation duration
• May indicate irrigation system limitations
• Check for soil layers restricting downward water movement

Pattern 2: All depths wet including deep

• Excellent irrigation - complete profile wetting
• Or possible over-irrigation if deep remains wet too long
• Monitor deep zone - should dry between irrigations

Pattern 3: Deep wet after irrigation, stays wet

• Over-irrigation - water wasted below root zone
• Reduce irrigation amount or frequency
• Causing nutrient leaching and water waste

Pattern 4: Deep dry, mid and shallow also dry

• Inadequate irrigation for extended period
• Irrigate promptly with adequate amount
• Consider deficit recovery irrigation strategy

Pattern 5: Deep wet continuously, shallow cycling

• Indicates water table presence or restricted drainage
• May affect crop selection and irrigation strategy
• Consider drainage improvement if problematic

Installation Guidelines

Selecting Installation Depth

The LT model is designed for deep zone depths:

• Mature orchards: 90-120 cm (36-48 inches)
• Established vineyards: 90-105 cm (36-42 inches)
• Drainage monitoring: Below typical root zone
• Deep-rooted crops: Within deepest active root zone

Installation Procedure

1. Auger deep hole: Use extension auger to reach required depth
2. Verify depth: Measure auger depth carefully
3. Prepare thick slurry: Mix native soil with water to thick consistency
4. Fill hole completely: Pour slurry to fill entire depth
5. Insert tensiometer: Push firmly, working through slurry to bottom
6. Confirm depth: Measure exposed tube to verify cup at target depth
7. Fill with water: Remove cap and fill tube to near top
8. Remove air bubbles: Tap tube firmly to release trapped air
9. Top off water: Refill after air removal
10. Seal: Replace and tighten cap securely
11. Mark and protect: Flag location, protect exposed tube from damage
12. Equilibrate: Wait 48-72 hours for deep zone equilibration

Special Installation Considerations

• Soil auger: Requires longer auger than standard
• Physical effort: Deep installation requires more effort
• Slurry consistency: Must be thick enough to support long installation
• Tube protection: Exposed tube longer, needs protection from equipment
• Location marking: Critical to mark well - easy to lose in field
• Access: Ensure accessible for regular monitoring

Reading and Maintenance

Monitoring Schedule

Frequency depends on use:

• Complete profile monitoring: Read with shallow and mid depths
• Drainage detection: Check 24-48 hours after irrigation
• Deep reserve tracking: Weekly during dry periods
• Research applications: Daily or as needed

Maintenance Requirements

Weekly Maintenance:

• Check water level in tube (inspect near top)
• Look for damage to exposed tube
• Verify gauge function
• Record readings

Bi-weekly Maintenance:

• Top off water if level dropped
• Check for air bubbles
• Tap tube if needed to release air
• Inspect cap seal

Monthly Maintenance:

• Remove cap and refill completely
• Check gauge accuracy
• Inspect for physical damage
• Verify tube integrity

Seasonal Maintenance:

• Deep tensiometers may need more frequent refilling
• Clean ceramic cup if response slows
• Replace water completely
• Check all connections and seals

Refilling Deep Tensiometers

Deep tensiometers use more water through the longer tube:

1. Check water level weekly
2. Remove cap when water level drops significantly
3. Fill completely to near top
4. Tap tube vigorously to release air bubbles
5. Top off after air removal
6. Replace cap securely
7. Monitor gauge returns to reading (may take longer at depth)

Multi-Depth Monitoring Strategy

Three-Depth System (Recommended)

Shallow (SR, 6-12”):

• Primary root activity zone
• Quick irrigation response
• Triggers irrigation timing

Mid (MLT, 18-24”):

• Water storage zone
• Verifies irrigation penetration
• Monitors profile wetting

Deep (LT, 36-48”):

• Deep storage monitoring
• Drainage detection
• Over-irrigation warning
• Deep root zone for mature plants

Benefits of Including Deep Monitoring

• Complete picture: Full root zone moisture profile
• Prevent water waste: Detect over-irrigation early
• Optimize application: Apply right amount, not excess
• Environmental protection: Prevent nitrate leaching
• Cost savings: Reduce wasted water and nutrients
• Mature plant management: Ensure deep roots have water access
• System evaluation: Verify irrigation system performance

Interpreting Deep Zone Behavior

Normal Patterns

• Responds slower than shallow: Normal due to depth
• Stays drier longer: Less evapotranspiration at depth
• Wets after shallow/mid: Water takes time to percolate down
• Buffer effect: Changes less rapidly than surface

Warning Signs

• Frequent wetting: May indicate over-irrigation
• Never dries: Possible water table or excessive irrigation
• No response to irrigation: Water not reaching this depth
• Extremely dry when others wet: Irrigation insufficient

Orchard and Vineyard Applications

Mature Trees

• Deep roots access water at 3-4 feet depth
• LT monitors this critical zone
• Ensures irrigation reaches entire root system
• Prevents deep stress in drought

Regulated Deficit Irrigation (Vineyards)

• Monitor controlled stress at depth
• Manage water stress for quality
• Ensure stress not excessive
• Maintain adequate deep reserves

Young Tree Establishment

• Initially may show little response
• As roots grow deeper, becomes more useful
• Helps encourage deep rooting
• Monitors irrigation depth increase as trees mature

Drainage and Water Quality

Over-Irrigation Detection

Deep tensiometer alerts to over-irrigation when:

• Readings stay consistently wet (0-20 cb)
• Wets immediately after every irrigation
• Never dries between irrigations
• Indicates water waste and nutrient leaching

Environmental Benefits

Preventing deep percolation protects:

• Groundwater quality: Reduces nitrate contamination
• Water resources: Prevents waste of irrigation water
• Energy: Reduces pumping for excess water
• Soil health: Maintains optimal soil structure

Troubleshooting Deep Tensiometers

Gauge Stays at Zero:

• May indicate saturated zone or water table
• Check mid and shallow readings for context
• Could indicate excessive irrigation
• Verify cup not installed in water table

Very Slow Response:

• Normal for deep installation - allow more time
• May need 48-72 hours to respond to irrigation
• Check shallower tensiometers respond first
• Verify water actually reaching this depth

Gauge Stays at 80 cb:

• Deep zone very dry (may be normal)
• Check shallow and mid for context
• If all dry, irrigate promptly
• If shallow/mid adequate, may indicate insufficient depth

Different from Shallower Depths:

• Normal - depth differences expected
• Use pattern for irrigation assessment
• Indicates water distribution profile
• Key information for irrigation management

Advanced Applications

Water Balance Studies

• Monitor deep drainage component
• Measure water losses below root zone
• Calculate irrigation efficiency
• Research water use patterns

Irrigation System Evaluation

• Verify system applies enough water for complete wetting
• Detect distribution problems
• Assess system capacity adequacy
• Evaluate emitter/sprinkler performance

Soil Characterization

• Identify soil layering affecting water movement
• Detect restrictive layers
• Assess drainage characteristics
• Understand soil water dynamics

Climate Adaptation Research

• Monitor deep soil water reserves
• Study root depth changes
• Evaluate deficit irrigation strategies
• Assess water conservation practices

Seasonal Management

Spring

• Reinstall after winter storage
• Monitor soil profile recharge from winter rain
• Establish baseline for coming season
• Adjust depths if needed

Summer

• Critical period for deep zone monitoring
• Watch for over-irrigation
• Verify adequate irrigation depth
• Monitor deep reserves during peak demand

Fall

• Track seasonal moisture changes
• Monitor deep zone as irrigation reduces
• Prepare for winter removal in cold climates
• Document season performance

Winter

• Remove in freezing climates
• Clean and inspect all components
• Store cups submerged in water
• Plan next season strategy

Economic and Environmental Benefits

Water Savings

• Detect and eliminate over-irrigation
• Reduce deep percolation losses
• Save 15-30% of water through deep monitoring
• Lower pumping costs

Fertilizer Efficiency

• Prevent nitrate leaching below root zone
• Improve nutrient use efficiency
• Reduce fertilizer costs
• Protect groundwater quality

Crop Performance

• Ensure deep roots have water access
• Prevent deep stress in mature plants
• Optimize water distribution
• Improve drought resilience

Professional Use

Essential for:

• Commercial orchard managers
• Vineyard irrigation specialists
• Agricultural consultants
• Water management districts
• Irrigation system designers
• Research scientists
• Environmental agencies
• Teaching and demonstration

Quality and Support

Irrometer LT tensiometers feature:

• Made in USA
• Quality tested
• Proven field durability
• Replaceable parts available
• Technical support
• Over 70 years of innovation
• Extensive documentation and resources