Diffusive reflectance spectroscopy for precise analysis of soils: An overview

Abstract

Soil testing plays a vital role in modern agriculture, helping in optimizing crop yield and sustainable land management. Traditional methods are often labor-intensive and time-consuming, which lead to the exploration of rapid alternatives such as diffusive reflectance spectroscopy [DRS]. DRS focus on the interaction of light with materials, utilizes the diffusely reflected radiation to glean insights into the optical properties of the sample. Unlike specular reflection, diffuse reflection occurs in all directions, making it ideal for analyzing rough-surfaced materials like soils. DRS instruments are equipped with integration spheres or diffuse reflectance attachments, they measure the spectral reflectance properties of soil samples, with optical fibers facilitating transmission to the spectrometer for analysis. In soil testing, DRS offers rapid and non-destructive assessment of soil properties. It estimates nutrient levels, organic carbon content, clay minerals, soil moisture, and salinity by exploiting the unique spectral fingerprints of soil constituents. This facilitates informed decision-making regarding fertilization, irrigation, and soil conservation practices. Future research aims to enhance the precision and feasibility of DRS in agriculture. Combining visible near-infrared [VNIR] and mid-infrared [MIR] spectra improves predictive capabilities, while calibration using spectral data from smallholder farms enhances model accuracy. Standardization of methods and protocols is crucial for ensuring consistency and reliability in soil testing procedures. Despite its benefits, DRS presents challenges in soil analysis. The complex and variable nature of soil matrices complicates the development of accurate calibration models, requiring standardized procedures and reference materials. Additionally, the need for a large number of samples and expertise in data processing may hinder widespread adoption of DRS in soil science.