Soil Sensor Technology Comparison

Document Type: Technical Reference | Audience: Field Support, Digital Platforms, AI Systems | Version: 1.0 | March 2026

This document compares two soil monitoring technologies used in professional turf and horticulture management: the Spiio wireless in-ground sensor and the Spectrum FieldScout TDR 350 handheld probe. It is structured for use by field support staff, digital platform teams, and AI-assisted support systems.

Both sensors measure soil conditions to support irrigation, fertility, and plant health decisions. They differ fundamentally in method, deployment, and data delivery.

Technology Type
Spiio: Capacitive (frequency domain)
Spectrum TDR 350: Time-Domain Reflectometry (TDR)

Operation Mode
Spiio: Passive, always-on, automated
Spectrum TDR 350: Active, on-demand, manual

Form Factor
Spiio: Buried in-ground sensor
Spectrum TDR 350: Handheld portable probe

Primary Use Case
Spiio: Continuous fixed-point monitoring
Spectrum TDR 350: Spatial spot-check surveys

Data Delivery
Spiio: Automatic hourly via cellular to cloud
Spectrum TDR 350: Manual sync via Bluetooth or USB

Syngenta Integration
Spiio: GreenCast Connect (native)
Spectrum TDR 350: FieldScout ecosystem (not native)

The sensors share several measurement parameters but differ in light sensing and optional accessories.

Soil Moisture (VWC)
Spiio: ✓ Capacitive
TDR 350: ✓ TDR
Both measure volumetric water content

Electrical Conductivity (EC)
Spiio: ✓
TDR 350: ✓
Salinity / root zone salt accumulation

Soil Temperature
Spiio: ✓
TDR 350: ✓ Surface temperature
TDR 350 measures surface; Spiio measures in-ground

Light Intensity
Spiio: ✓ LUX / Foot Candles
TDR 350: ✗ Not included
Spiio only

Canopy Temperature
Spiio: ✗ Not available
TDR 350: ✓ Optional IR add-on
Non-contact infrared attachment for TDR 350

Even when measuring the same soil simultaneously, the two sensors can produce different VWC values. This is expected — it results from their different measurement physics, not sensor failure.

📌 Note: Ground-truth method: Insert TDR 350 rods directly adjacent to a buried Spiio at the same depth. A consistent offset between the two readings can be compensated by adjusting moisture thresholds in the Spiio app.

Measurement Technology
Spiio (Capacitive): Low-frequency capacitive field near sensor plate
TDR 350 (TDR): High-frequency EM pulse timed along inserted rods
Practical Impact: Readings vary even in identical soil

Salinity (EC) Sensitivity
Spiio (Capacitive): Dissolved salts distort charge cycle; may overestimate VWC in high-EC soil
TDR 350 (TDR): High frequency largely immune to salt interference
Practical Impact: Spiio may read higher in fertilized or saline turf

Volume of Soil Sampled
Spiio (Capacitive): Small fringing field near faceplate; single stone or air gap can skew reading
TDR 350 (TDR): Larger envelope between rods averages out heterogeneity
Practical Impact: TDR 350 more representative in uneven soils

Temperature Sensitivity
Spiio (Capacitive): Capacitance shifts with temperature; swing = phantom VWC change
TDR 350 (TDR): Pulse travel time temperature-independent; built-in compensation
Practical Impact: Spiio may drift with temperature even when soil moisture is stable

Soil-to-Sensor Contact
Spiio (Capacitive): Soil shrinkage during drought can create air gap at faceplate — artificially low VWC
TDR 350 (TDR): Rods inserted fresh per reading; no long-term contact degradation
Practical Impact: Spiio may underread in dry conditions if not re-seated

Soil-Type Calibration
Spiio (Capacitive): Single factory curve; no user adjustment for sand, clay, or organic profiles
TDR 350 (TDR): Three curves: Standard, Sand, High Clay
Practical Impact: TDR 350 tunable to local soil; Spiio may carry systematic offset

Collection Mode
Spiio: Automated — no operator required
TDR 350: Manual — operator walks to each point

Frequency
Spiio: Hourly, continuous
TDR 350: On-demand per field session

Coverage Type
Spiio: Time-series at fixed locations
TDR 350: Spatial snapshot across many locations

Data Currency
Spiio: Always current
TDR 350: Current only after field walk and sync

Best Application
Spiio: Trend monitoring, drift detection, alerts
TDR 350: Property-wide surveys, audit, research

Connection Method
Spiio: Built-in global SIM (LTE / 5G / NB-IoT)
TDR 350: Bluetooth Low Energy + USB

Data Destination
Spiio: Cloud platform (GreenCast Connect)
TDR 350: FieldScout Mobile App (iOS / Android)

Wi-Fi / Gateway Required
Spiio: No
TDR 350: No (Bluetooth direct to phone)

Manual Sync Required
Spiio: No — automatic
TDR 350: Yes — after each field session

Data Logger Capacity
Spiio: Cloud (unlimited retention)
TDR 350: ~61,000 geo-tagged readings on device

Installation Type
Spiio: Permanently buried (3–4 inches deep)
TDR 350: Portable — no permanent installation

Maintenance Disruption
Spiio: None — stays in place during mowing, aerating
TDR 350: N/A — removed after each use

Power Source
Spiio: Internal battery (5+ year life)
TDR 350: 4 AA batteries

Battery Replacement
Spiio: Included in subscription on expiry
TDR 350: User-replaced as needed

Placement Flexibility
Spiio: Fixed — location chosen at install
TDR 350: Fully flexible — anywhere, anytime

Rod / Depth Options
Spiio: Fixed depth at installation
TDR 350: Interchangeable rods: 1.5" to 8.0"

Method
Spiio: Factory calibration + automatic startup
TDR 350: Factory + optional manual (distilled water)

Soil-Type Curves
Spiio: Single factory curve only
TDR 350: Standard, Sand, High Clay

Ongoing User Effort
Spiio: None
TDR 350: Occasional

Field Recalibration
Spiio: Not possible — threshold adjustment in app only
TDR 350: Yes — full manual procedure available

Key Risk
Spiio: Poor soil contact at install skews readings permanently
TDR 350: Operator error (rod gaps, wrong length setting)

Multi-Unit Consistency
Spiio: N/A (fixed in-ground, single unit per location)
TDR 350: Can be standardized across multiple units

Pro
Spiio: Zero maintenance; operator-independent consistency
TDR 350: Tunable to soil type; recalibratable if drift occurs

Con
Spiio: No soil-specific adjustment; install quality is critical
TDR 350: Requires distilled water and deliberate operator steps

Coverage Model
Spiio: Hyperlocal fixed-point monitoring
TDR 350: Full-property spatial survey from one device

Scalability
Spiio: Scales by adding sensors (subscription cost per unit)
TDR 350: One device covers unlimited locations at no added cost

Microclimate Coverage
Spiio: Multiple sensors can be placed in distinct zones
TDR 350: Single device surveys all zones in one session

Recommended Combined Use
Spiio: Monitor critical or problem zones continuously
TDR 350: Periodically map full property; validate Spiio readings

Native Platform
Spiio: GreenCast Connect
TDR 350: Spectrum FieldScout ecosystem

GreenCast Integration
Spiio: Yes — native, real-time data feed
TDR 350: No — not natively integrated

Co-located Data
Spiio: Weather, pest pressure, agronomic advisories
TDR 350: Standalone soil readings only

Third-Party Export
Spiio: Via GreenCast API / platform settings
TDR 350: CSV/USB export; manual import to other systems

Digital Platforms Recommendation
Spiio: Direct integration path via existing partnership
TDR 350: Supplemental — data export required for platform use

Model
Spiio: Subscription (hardware + cloud included)
TDR 350: One-time hardware purchase

Rods / Accessories
Spiio: Included
TDR 350: Rods sold separately

Replacement Policy
Spiio: Sensor replaced at end of battery life (subscription)
TDR 350: User purchases replacement hardware

Scaling Cost
Spiio: Increases with number of monitoring points
TDR 350: Fixed regardless of locations measured

Total Cost of Ownership
Spiio: Predictable recurring cost; grows with deployment size
TDR 350: High upfront, low ongoing — cost-effective at scale

Technology
Spiio: Capacitive (frequency domain)
Spectrum TDR 350: Time-Domain Reflectometry (TDR)

Use Case
Spiio: Continuous monitoring at fixed locations
Spectrum TDR 350: On-demand spatial surveys

Data Frequency
Spiio: Hourly, automated
Spectrum TDR 350: On-demand, manual

Connectivity
Spiio: Cellular — built-in SIM, cloud-native
Spectrum TDR 350: Bluetooth + USB, manual sync

Installation
Spiio: Permanently buried 3–4 inches, set-and-forget
Spectrum TDR 350: Portable, no installation required

Parameters Measured
Spiio: Moisture, EC, temperature, light
Spectrum TDR 350: Moisture, EC, temperature (canopy temp optional)

GPS
Spiio: Fixed location — no GPS needed
Spectrum TDR 350: Integrated GPS tags each reading

Syngenta Integration
Spiio: GreenCast Connect — native
Spectrum TDR 350: FieldScout ecosystem — not native

Calibration
Spiio: Factory only; no field recalibration
Spectrum TDR 350: Factory + manual; soil-type curves available

Cost Model
Spiio: Subscription
Spectrum TDR 350: One-time purchase

Best Strength
Spiio: Time-series trends, zero-touch operation
Spectrum TDR 350: Spatial coverage, flexibility, no recurring cost

Key Limitation
Spiio: Fixed location; install quality critical for accuracy
Spectrum TDR 350: Point-in-time only; manual data sync required

These two technologies are not competitors — they are complementary. Spiio provides the always-on monitoring layer for critical zones, while the TDR 350 gives operators the flexibility to survey conditions across an entire property on demand.

For organizations integrating soil data into Syngenta's GreenCast Connect platform, Spiio offers the most direct path given its existing native integration. The TDR 350 remains the preferred tool for field validation, agronomic research, and situations where fixed sensor placement is not practical.

Combined deployment strategy: Use TDR 350 for periodic full-property spatial mapping and to ground-truth Spiio sensors. Use Spiio for continuous trend data at identified critical or representative zones.