Diagnostic horizons in the Russian soil classification system

The analysis of the responses of users of the substantive-genetic Russian soil classification system revealed some problems concerning the genetic (diagnostic) horizons. Applying horizons is essential since soil diagnostics are based on their identification and their combinations in soil profiles. In the recent Russian system, there are many diagnostic horizons, and their recognition is not always easy. This review is aimed at displaying the main elements and the genetic essence of the horizons, as well as the reasons to choose the diagnostic criteria and parameters for most of them. The horizons are grouped into genetic sets, and the specific properties of the horizons are emphasized, as well as the differences between the horizons and the feasibility to introduce new horizons. A rough comparison of the diagnostic horizons in the Russian and WRB systems revealed the considerable similarity of the taxa, whose definitions depend on the presence of the diagnostic horizons: these are the orders and soil reference groups, respectively.