Institutional Digital Repository (Indian Institute of Technology Kharagpu)

V, Lavanya

DEVELOPMENT OF A LOW-COST SMARTPHONE-INTEGRATED PORTABLE 
IMAGING DEVICE FOR THE DETERMINATION OF NITRATE AND PHOSPHATE IN 
SOIL AND WATER  
NAME: LAVANYA V 
ROLL NUMBER: 19AG91R03 
SUPERVISOR NAME: DR. SOMSUBHRA CHAKRABORTY 
 
ABSTRACT 
This research presents a smartphone-integrated imaging device to detect phosphate (PO4
3-) and nitrate 
(NO3
-) in soil and water samples for agricultural input management and environmental pollution 
monitoring. This low-cost and field-deployable device uses a smartphone with a camera to take a color 
photograph of the solution under test. The sensing principle is based on the standard colorimetric 
phenoldisulfonic acid, Chromotropic acid, and ascorbic acid methods for NO3
- and PO4
3- in soil and 
water samples, respectively. A 3D printed device that houses the optical components is coupled to the 
phone's built-in rear camera and turned into a compact handheld system. An android application, 
'SMART NP,' is also developed to quantify the concentrations of NO3
- and PO4
3- in soil and water 
samples using the Value (V) component of the HSV color space model. The results obtained with the 
proposed device were comparable to laboratory-grade spectrophotometer data. The limit of detection 
of the device for NO3
- in soil, NO3
- in water, PO4
3- in soil, and PO4
3- in water were calculated as 0.1 
mg L-1, 0.07 mg L-1, 0.001 mg L-1, and 0.02 mg L-1, respectively, with good accuracy (≤1% bias) and 
precision (~2% residual standard deviation). The device exhibited a sensitivity of 0.17 mg L-1, 0.12 
mg L-1, 0.026 mg L-1, and 0.49 mg L-1 for NO3
- in soil, NO3
- in water, PO4
3- in soil, and PO4
3- in water, 
respectively. Using the Chromotropic acid method, the limit of detection was calculated as 0.1 mg L-
1 with a sensitivity of 0.26 mg L-1. The device showed a bias of 0.9% and a precision of 1.95%, 
indicating its reliability. Additionally, the device-predicted soil NO3
- data, combined with kriging 
interpolation, showcased spatial variability in soil NO3
- levels at the regional level, and the device was 
also used for estimating soil available P and applying DSM techniques to create high-resolution soil 
available P maps. Overall, this sensing device has the potential to assist farmers or scientists in easily 
measuring NO3
- and PO4
3- concentrations in soil and water media, without the need for laboratory 
equipment. 
 
Keywords: soil; water; nitrate; phosphate; smartphone, imaging device; HSV; kriging; DSM 
 


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