I am curious of the lower boundary of soil. Soil is formed after a long complex processes and it has been through coevolution with living organisms. According to the USDA, for soil classification, the lower boundary of soil is arbitrarily set at 2 m. So, this is obviously not the actual depth. Yost and Hartemink (2020), in a review article mentioned soil depth/thickness:
A general term for the vertical dimension of the soil. Some authors consider it includes only the solum, some others include the solum plus the C and the G horizons (whether they represent or not the soil parent material), and some others consider it as equivalent to the root-restricting depth.
Considering C horizon while calculating the soil depth is also stated in a research by Richter and Markewitz(1995). They have mentioned varying depth of soils from 20 m to 100 m depending on spatial variations in climatic features. So, till which distance from our earth's surface is soil? Is there any standard depth of soil?
- Yost, J.L., Hartemink, A.E. (2020). How deep is the soil studied – an analysis of four soil science journals. Plant Soil 452, 5–18. https://doi.org/10.1007/s11104-020-04550-z
- Richter, D., & Markewitz, D. (1995). How Deep Is Soil? BioScience, 45(9), 600-609. doi:10.2307/1312764