Soil is a complex matrix made of organic and inorganic mineral matter, water, and air. The organic material ranges from decomposed and stable humus to fresh particulate residues from different sources [1]. Texture affects soil behavior (e.g., water holding capacity, nutrient retention and supply, drainage, and nutrient leaching [2]) and depends on the proportion by weight of the sand, silt, and clay it contains. Cation-exchange capacity (CEC), a measure of the ability to hold positively charged ions, influences soil structure stability, nutrient availability, pH, and its reaction to fertilizers and other ameliorants. The main ions associated with CEC in soils are Ca²⁺, Mg²⁺, Na⁺, and K⁺ [3]. Soil pH directly influences the availability of nutrients to plants, microbial activity, and overall soil health, affecting plant growth, crop yields, and the sustainability of agricultural practices. This study describes how organic matter content, pH value, silt, clay and sand content, exchangeable calcium and magnesium, and limestone content were measured in soil in seconds by using near-infrared spectroscopy (NIRS).

The obtained NIR spectra of soil samples (Figure 1) were used to create prediction models for the quantification of organic matter, pH, silt, sand, limestone, clay, and exchangeable calcium and magnesium. The quality of the prediction models was evaluated using correlation diagrams
(Figures 2–9) which display a high correlation between the NIR prediction and the reference values measured with standard methods described in
Table 1. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.

This Application Note displays the benefits of using NIR spectroscopy for soil analysis. All the presented soil quality parameters can be measured simultaneously in only a few seconds. Compared to other conventional methods (Table 1), near-infrared spectroscopy soil analysis requires no sample preparation nor solvents. This ultimately leads to a reduction in workload and related costs, as well as keeping lab personnel safer.