Current Crop and Soil Sensors for Precision Agriculture

Precision agriculture relies on real-time monitoring of crop and soil conditions to optimize inputs like water, nutrients, and pesticides. Sensors are key tools that help farmers gather accurate field data, reduce costs, and improve sustainability. These sensors are used both in protected cultivation (greenhouses) and in open-field farming.

Soil Sensors in Precision Agriculture

a. Soil Moisture Sensors

• Function: Measure volumetric water content in soil.
• Applications: Irrigation scheduling, water-use efficiency.
• Examples: Decagon 5TE, Sentek Drill & Drop probes.

Types:

• Tensiometers: Measure soil water tension (availability to plants).
• Capacitance sensors (Frequency Domain Reflectometry, FDR): Detect dielectric constant changes related to water content.
• Time Domain Reflectometry (TDR): Measure the travel time of an electromagnetic pulse in soil.

b. Soil pH Sensors

• Function: Monitor soil acidity or alkalinity.
• Principle: Glass electrode or ion-selective electrodes.
• Applications: Fertilizer management, nutrient availability assessment.
• Examples: Bluelab Soil pH Pen, Hanna Instruments HI981030.

c. Soil Electrical Conductivity (EC) Sensors

• Function: Measure dissolved salts in soil solution (indicator of salinity/fertility).
• Types: Contact probes, electromagnetic induction (EM38).
• Applications: Salinity mapping, variable-rate fertilizer application.
• Examples: Veris EC Mapper, Delta-T Devices WET Sensor.

d. Soil Temperature Sensors

• Function: Monitor root-zone temperature.
• Principle: Thermistors or thermocouples.
• Applications: Germination, microbial activity, nutrient uptake.
• Examples: DS18B20 digital soil temp sensor, Apogee ST-100.

e. Nutrient Sensors (Ion-Selective Electrodes, Optical Sensors)

• Function: Detect specific ions like nitrate, potassium, ammonium, and phosphate.
• Applications: Fertigation and nutrient management.
• Examples: Ion Selective Field Effect Transistors (ISFET), Nutrisense sensors.

Crop Sensors in Precision Agriculture

a. Chlorophyll / SPAD Meters

• Function: Measure leaf chlorophyll content (proxy for nitrogen status).
• Applications: Nitrogen management, fertilizer scheduling.
• Examples: SPAD-502 Plus (Konica Minolta).

b. Multispectral and Hyperspectral Sensors

• Function: Capture reflectance in visible and near-infrared (NIR) bands.
• Applications: Plant health, disease detection, stress monitoring.
• Examples: MicaSense RedEdge, Parrot Sequoia.

c. Canopy Temperature Sensors

• Function: Infrared sensors measure leaf surface temperature.
• Applications: Early water stress detection.
• Examples: Infrared Thermometers, Apogee SI-111.

d. NDVI (Normalized Difference Vegetation Index) Sensors

• Function: Measure crop vigor and biomass by comparing red and NIR reflectance.
• Applications: Yield prediction, variable-rate input application.
• Examples: GreenSeeker, Crop Circle.

e. Fluorescence Sensors

• Function: Detect chlorophyll fluorescence as an indicator of photosynthetic activity.
• Applications: Stress detection, photosynthesis efficiency.
• Examples: Multiplex sensor, PAM fluorometers.

f. Biosensors (Emerging)

• Function: Detect specific plant metabolites, pathogens, or stress markers.
• Applications: Early disease diagnosis, precision input application.
• Examples: Nano-biosensors for pathogen detection.