Impact of Commercial Soil Additives on Microbial Activity and Carbon Isotopic Characteristics of Recultivated Post Lignite Mine Soils

Abstract

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.