Instrumentation & Measurement Magazine 24-3 - 55

Fig. 5. Plant growth monitoring with RFID sensing technology.
Fig. 4. Block diagram of a typical RFID soil moisture sensor.

soil [80], [81]. Fig. 4 shows the block diagram of a typical RFID
soil moisture sensor.
Soil pH level plays an important role in plant growth. The
solubility of the nutrients and the micro-organism activities
of the plant roots are greatly dependent upon the pH level
of the soil [82]. For instance, the uptake of the micronutrients
increases when the soil is acidic, and the uptake of the macronutrients increases when the soil is alkaline. These micro and
macronutrients play an important role in defining the plant
traits, such as height, biomass, number of flowers, size of flowers and pollen production [82]. One such study was conducted
to develop a low-cost, chipless passive (UWB) RFID pH sensor. The chitosan hydrogel was used to define the behavior
of pH properties. The sensor can operate within the range of
800-860 MHz, and the pH sensor can accurately measure any
values between pH 4-7 [83]. Table 7 presents typical examples
of the applications of RFID sensors to the monitoring of soil
conditions. The work presented in the literature depicts that
chip-based, chipless, and add-on sensors have been explored
in the soil monitoring studies for smart agriculture. In theory,
antenna type RFID sensors can also be explored for such applications. The lack of this is probably because the soil conditions
significantly affect the antenna performance and thus hinder
signal communication and processing.

Plant Growth Monitoring
Generally speaking, plant growth refers to the increase in the
plant's height, size, lateral spread, number of flowers, fruits/
vegetables, and so on. A study on the survival and growth of

grapevines by implanting chip-based RFID tags within the
plants was conducted. The tags were implanted at the roots
within the range of 30 cm from each other. The depth of the insertion of the microchip in the roots varied from 3 cm to 4 cm of
the grafting. The data obtained from the micro-chips were analyzed through SprintDB software. Histological observations
were also made through embedded camera sensors in the micro-chips, and the images of vascular tissues were acquired.
The image analysis shows that RFID based micro-chips were
very useful for plant growth monitoring and also to ensure if
the plant is healthy or not. Fig. 5 presents a plant monitoring
system with RFID [84], [85]. Another study was performed on
the growth monitoring system for sugarcane with the aid of
RFID, ZigBee, video processing technologies, and automatic
control. The monitoring system is designed by incorporating the characteristics of the sugarcane. The developed system
could monitor the temperature, humidity, and other growing
conditions very well and can aid in the management process
of precision agriculture [40]. Additionally, multi-function remote sensing with spectral imaging and an environmental
sensing RFID system was developed for cabbage seedling
management in the greenhouse. The system could measure the
illumination, temperature, humidity, and soil moisture, which
could help the farmers to understand the crop conditions and
growth. Therefore, the addition of the developed system could
improve the management and the cultivation system [86].
The required parameters for plant growth monitoring include the lateral height of the plant, radius, size of the leaf,
size of flowers and petals as well as the fungal diseases of the
plants. The existing literature shows that RFID sensors can effectively measure the growth of the roots. The height, size, and

Table 7 - Example of applications of RFID sensors for monitoring soil conditions
Measurement
range

Sensitivity

Soil temperature
[74]

-25-100 °C

15%

Add-on RFID
sensors

13.56 MHz

Soil moisture [75]

Add-on RFID
sensors

2.4 GHz

≥100 °C/ppm

0.055 g/L

Chip-based RFID
sensors

9.6 MHz-1.1 GHz

pH 4-10

pH 7.7-7.8

Chipless RFID sensors

3 GHz-7 GHz

Parameters

Soil salinity [80]
Soil pH [83]

May 2021

Sensor type

Operating
frequency

Detection
distance
40 cm
1.2 m
309.50 mm
-

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Instrumentation & Measurement Magazine 24-3

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