Vis–NIR-based optical sensor system for estimation of primary nutrients in soil

Abstract

A Vis–NIR-based optical sensor system for monitoring of soil nutrients has been developed in this work. This instrument allows the measurement of three nutrients: nitrogen, phosphorous and potassium in soil. The sensing is based on the diffused reflectance obtained from the sample when illuminated with source of appropriate wavelength. Based on extensive experimentation and analysis, the selectivity of the nutrients to specific wavelengths was found to be 850 nm for nitrogen, 620–630 nm for phosphorous and 460–470 nm for potassium. These three wavelength ranges have been selected considering the cross-sensitivity issue such that the sensor response to a target nutrient does not interfere with other nutrients present in the sample. Distinct mathematical models were developed for each of the three nutrients based on the reflectance characteristics curves of the nutrients. A full description of the instrument, methodology adopted, mathematical modelling and characterization has been carried out and is reported here. The response behavior of the system was studied based on parameters such as repeatability, reproducibility, sensitivity, linearity, R2, root-mean-square error, standard error of estimate and limit of detection. The results obtained validate the satisfactory performance of the system in monitoring soil nutrients and the promising future application in precision agriculture and site-specific crop management systems.