Dissolution and re-crystallization processes of active calcium carbonate in soil developed on tufa

Carbonates are an important component of soil found in dry regions. The main aim of this paper is to investigate the origin of C in soil carbonate and to assess the effect of applied organic residues on carbonate dissolution and crystallization. We measured the δ¹³C of organic carbon (OC), active and total carbonates down to a depth of 260 cm of a calcareous soil developed in a tufa deposit. We found a parallel decrease of the active CaCO₃-δ¹³C and OC-δ¹³C from -10.5 to -13.6‰ and from -24.6 to -26.4‰, respectively, in the soil profile. Furthermore, the active CaCO₃-δ¹³C and the concentrations of Ca and Mg in the soil solution during incubation of soil samples from the top 0- to 10-cm layer (soil δ¹³C = -11.5‰) with and without addition of pasteurized chicken manure (PCM, -23.2‰) were determined. The active CaCO₃- δ¹³C wasn't affected by time and treatment and with a δ¹³C 14.1‰ higher than the soil organic matter (SOM). The sum of soil solution Ca and Mg concentrations in the PCM treatment decreased in the first days of the incubation and then increased linearly due to released protons by the nitrification processes. The tufa and the soil formed on it have two likely sources for the C in the active carbonate fraction; biogenic carbonates deposited during tufa formation and SOM mineralization and re-crystallization of soil carbonates. Application of an N-rich amendment to this calcareous soil enhanced the dissolution and re-crystallization of calcium carbonate.