**5. Conclusions**

The objective of this review was to summarize the progress made during the last decade using laboratory and proximal soil sensing in the VNIR-SWIR region for SOC estimations. Laboratory measurements are considered to be a well-established method for soil properties estimations, but there is not ye<sup>t</sup> a commonly accepted universal model with broad application. The attention that soil

spectroscopy has gained is evident on the efforts of creating SSLs worldwide, albeit, with a nonagreed protocol. Research has also been made towards the use of proximal soil sensors for in situ applications that could estimate SOC in real time and on larger spatial scales. Overall, the results are promising for SOC estimations, and more research needs to be done in terms of selecting the proper spectral range of the sensor, the preprocessing methods, and the calibration techniques. Detrimental effects such as soil moisture, soil roughness, vegetation cover, and others that affect SOC spectral response need to be addressed for model transferability from laboratory to in field applications. Due to the various inconsistencies among studies, it is suggested that articles should include more information about the experimental design, the criteria used for the selection of the chemometric approach, and the pre- and post- processing procedures to facilitate comparisons of results among studies. The advent of much smaller and more affordable spectrometers could potentially provide even more rapid soil properties estimations to assist farmers in selecting the most appropriate managemen<sup>t</sup> practices with respect to soil preservation.

**Author Contributions:** Conceptualization, T.A., D.B., and G.Z.; methodology, T.A., A.B.; formal analysis, T.A. and D.B.; investigation, T.A. and D.B.; resources, T.A. and A.B.; writing—original draft preparation, T.A., A.B.; writing—review and editing, D.B. and G.Z.; supervision, D.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the project "Research Synergy to address major challenges in the nexus: energy-environment-agricultural production (Food, Water, Materials)"—NEXUS, funded by the Greek Secretariat for Research and Technology (GSRT)—Pr. No. MIS 5002496.

**Conflicts of Interest:** The authors declare no conflict of interest.
