Biophysical Plant Tissue Measurement
Biophysical plant tissue measurement refers to non-destructive, often rapid techniques
that assess
the physical or physiological properties of plant tissue to infer its nutritional, water, or health
status.
Unlike chemical analysis, these methods typically do not involve tissue destruction or complex lab
procedures.
Common Techniques & Principles:
1. Chlorophyll Meters (e.g., SPAD, Dualex, YARA N-Tester):
- Measures: Leaf chlorophyll content
(optical absorbance).
- Infers: Nitrogen status, as chlorophyll
and N are highly correlated.
- Use: In-season N management, detecting
deficiency.
2. Leaf/Canopy Reflectance Sensors (e.g. Greenseeker) & Multispectral
Imaging:
- Measures: Reflectance of light at
specific wavelengths (visible, near-infrared).
- Infers: Chlorophyll content, biomass,
water stress, nutrient imbalances (via spectral indices
like NDVI, NDRE).
- Use: Precision agriculture, variable-rate
application, stress mapping.
3. Ion-Specific Electrodes (e.g., Nitrate Probes):
- Measures: Concentration of specific
ions (e.g., NO₃⁻, K⁺) in extracted sap.
- Infers: Immediate nutrient availability
in the plant.
- Use: Quick sap testing for real-time
nutrient status.
4. X-ray Fluorescence (XRF) Spectrometry:
- Measures: Elemental composition by
detecting emitted secondary X-rays.
- Infers: Concentrations of multiple
elements (e.g., P, K, Ca, heavy metals).
- Use: Rapid, multi-element analysis
without extensive sample preparation.
5. Specific Wavelength Reflectance (e.g. NN-Easy Mn-Tester, Spectracrop
P-Tester)
- Measures reflectance of physiological
processes induced by light after a period of inactivity in
the dark
- Infers: Qualitative results depicting
deficiency, critical values, and sufficiency for Manganese
(Mn), and Phosphate (P).
- Use: Each Element is measured with
a separate handheld instrument, or both measurements
are combined in one instrument (nwewer Version. Both, direct measurements in the field and
after transport to some other location are possible. Internet connection is a must for data
processing which is independent of the measurement and can be done any time later.
Advantages:
- Non-destructive & rapid: Allows
repeated measurements on the same plant over time.
- High-throughput: Suitable for field
scouting and large-scale sensing.
- Real-time data: Enables immediate
management decisions (e.g., fertigation adjustment).
Limitations:
- Often indirect: Measures a correlated
trait (e.g., chlorophyll) rather than the nutrient itself.
- Calibration needed: Requires local
calibration against standard chemical analysis.
- Environmental sensitivity: Readings
can be affected by light conditions, leaf thickness, water
status, etc.
- Limited to certain nutrients: Most
effective for N; less established for others like P, K, or
micronutrients.
Practical Application in Nutrient Management:
These tools are increasingly used for precision nutrient management, allowing farmers
to:
- Detect within-field variability in
crop nutritional status.
- Apply fertilizers site-specifically
based on real-time plant demand (e.g., variable-rate N
application guided by chlorophyll sensors).
- Monitor the effectiveness of fertilization
programs during the growing season.
In summary, biophysical plant tissue measurement complements traditional
chemical
analysis by providing fast, in-field diagnostics that support dynamic, data-driven nutrient
management decisions.
