Oliver Bens

The impact of commercial soil additives (CSA) on post lignite mine soils was assessed after 14 months of field application by evaluating the changes in microbial respiration, the respiratory quotient and the isotopic signature of microbial respired CO₂-C. Soil samples were randomly collected from 0 to 5 cm depths from: (1) tilled plots amended with polyacrylate hydrophilic polymer, mixed with zeolithes and bentonite (a-CSA) at 5,000 kg ha⁻¹ dry mass; (2) tilled plots amended with a near-natural digester compost enriched with mineral additives, bentonite and synthesized humic acids (b-CSA) at 10,000 kg ha⁻¹ dry mass; (3) plots tilled and without amendment (control), and (4) plots without tillage and amendment. All plots were seeded with orchard grass (Dactilus glomerata, L.). Soil microbial basal respiration was low and not significantly affected by the treatments presumably, due to low availability of CSA for microbial metabolism. Soil microbial respiration, respiratory quotients and ¹³C isotopic characteristics of the respired CO₂ followed a similar trend for all treatments throughout the incubation period and was not significantly different between a-CSA and b-CSA amended plots compared to the control and untilled plots. The results indicate that the current soil microbial communities have similar eco-physiology and substrate utilisation patterns, and may have met their metabolic requirements mainly from the inherent and recent organic matter input from the vegetation cover. This may be due to the recalcitrant nature of the CSAs or the recommended application rates being too low to affect any significant short-term biochemical impact on these recultivated soils in early stages of development.

Spatial variability of humus layer (O layer) thicknesses can have important impacts upon soil water dynamics, nutrient storage and availability, as well as plant growth. The purpose of the present study was to elucidate the impact of forest‐transformation practices on the spatial variability of O layer thicknesses. The study focused on the Kahlenberg forest area (NE Germany) with stands of Scots pine (Pinus sylvestris)and European beech (Fagus sylvatica)of different age structures that form a transformation chronosequence from pure Scots pine stands towards pure European beech stands. Topsoil profiles including both, the O layer and the uppermost humic mineral soil horizon were excavated at intervals of 0.4 m along 15–20 m long transects, and spatial variability of O layer thicknesses was quantified by variogram analysis. The correlation lengths of total O layer thickness increased in the sequence consisting of pure pine stand (3.1 m) → older mixed stand (3.7 m) → pure beech stand (4.5 m), with the exception of the younger mixed stand, for which no correlation lengths of total O layer thickness could be determined. The degree of spatial correlation,i.e., the percentage of the total variance which can be described by variograms, was highest for the two monospecies stands, whereas this percentage was distinctly lower for the two mixed stands. A similar minimum for the two mixed stands was observed for the correlation lengths of the Oh horizon. These results suggest that the spatial structures of forest‐transformation stands may be interpreted in terms of a disturbance (in the form of the underplanting of beech trees). After this disturbance, the forest ecosystem requires at least 100 y to again reach relative equilibrium. These findings are in line with the results of other soil‐related investigations at these sites.