Climate vs. parent material - Which is the key of Stagnosol diversity in Croatia?

- Most Croatian Stagnosols formed by top-down pedogenesis, but some are polygenetic.
- Argic horizon may have as much as 1.2 times more clay than the overlying horizon.
- Soil pH and base saturation were affected by precipitation gradient in the region.
- Soil clay content and CEC were affected by parent material heterogeneity.
- Soil mechanical and mineral compositions indicate more than one source of loess.

Stagnosols are the most widespread soils in the Pannonian region of Croatia. In Croatia they are referred to as Pseudogleys and considered to form primarily by normal (top-down) pedogenesis. However, the formation of their non-calcareous loess parent materials probably involved different sources, transports, and depositional environments. We aimed to determine the courses of soil formation and the characteristics of three Stagnosol profiles studied along the mean annual precipitation (MAP) gradient (700-1100 mm) in the Pannonian region of Croatia. We found that soil redoximorphic features formed in situ by ongoing pseudogleization. Vertical trends for the clay/silt and coarse/fine silt ratios pointed to top-down pedogenesis. However, high organic C content at the bottom of one soil profile is the result of erosion/sedimentation processes, whereas high clay content in the subsoil of another profile was largely the result of sedimentation in a shallow paleo-lake. Therefore, some Croatian Stagnosols should be considered polygenetic. Each soil profile was classified using the WRB system, and the new WRB-2014 version proved more suitable than the previous one (WRB-2006). However, suggestions for improvements are given. In line with the MAP gradient were several morphological and only two chemical (pH and base saturation) soil characteristics. Organic C content did not correspond to MAP due to variability of forest topsoils. Clay content and CEC did not agree with MAP due to variability of loess parent materials across the Pannonian region of Croatia. The existence of more than one source of loess material (confirmed by the modal analysis) and the differences in depositional paleo-environments resulted in slightly different mechanical compositions of the investigated parent materials. We concluded that both climate and parent material must be regarded as key factors for the formation and characteristics of Stagnosols in the Pannonian region of Croatia (and the wider southwestern Pannonian Basin).