Soil samples were leached 0 (non-leached), 5, 10, and 15 times and then analyzed to determine the contents of cations (Al3+, Ca2+, K+, and Mg2+), the total carbon content, and the pH. Eighty soil samples from the topsoil of plots located in central Poland were analyzed. The potential influence of the species composition of stands (beech and fir) was also investigated. Furthermore, near-infrared (NIR) spectroscopy was used to evaluate the properties of forest soils. This study investigated changes in the composition of the cation exchange capacity of soil samples caused by the acid leaching of soil cations under laboratory conditions. The development of the Global Soil Spectral Library might be a step in the right direction. To do this, research in soil spectroscopy needs to be more collaborative and strategic. For future work we recommend that research should focus on: (i) moving forward with more theoretical calibrations, (ii) better understanding of the complexity of soil and the physical basis for soil reflection, and (iii) applications and the use of spectra for soil mapping and monitoring, and for making inferences about soils quality, fertility and function. Many studies show that we also can predict properties such as pH and nutrients, although their robustness may be questioned. We conclude that the technique is useful to measure soil water and mineral composition and to derive robust calibrations for SOM and clay content. Field analyses and strategies for the practical use of vis–NIR are considered. We then discuss the performance and generalization capacity of vis–NIR calibrations, with particular attention on sample pretratments, covariations in data sets, and mathematical data preprocessing. A review of the past and current role of vis–NIR spectroscopy in soil analysis is provided, focusing on important soil attributes such as soil organic matter (SOM), minerals, texture, nutrients, water, pH, and heavy metals.
To this end, we describe the fundamentals of visible and infrared diffuse reflectance spectroscopy and spectroscopic multivariate calibrations. It should also provide critical discussion on issues surrounding the use of vis–NIR for soil analysis and on future directions. Our intention is for the review to serve as a source of up-to-date information on the past and current role of vis–NIR spectroscopy in soil science. This chapter provides a review on the state of soil visible–near infrared (vis–NIR) spectroscopy.
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