Stabilization of composted organic matter after application to a humus-free sandy mining soil

The use of mining substrates for recultivation purposes is limited due to t heir low organic matter (OM) contents. In a l-yr laboratory experiment we e valuated the stabilization of biowaste compost added to a humus-free sandy mining soil to examine the suitability of compost amendment for the formati on of stable soil organic matter (SOM). The stabilization process was chara cterized by measuring enrichment of OM and nitrogen in particle size fracti ons obtained after dispersion with different amounts of energy (ultrasonica tion and shaking in water), carbon mineralization, and amount of dissolved organic carbon (DOC). During the experiment, 17.1% of the organic carbon (O C) was mineralized. Organic carbon enrichment in the < 20-mum particle size fraction at the beginning of the experiment was in the range of natural so ils with similar texture. Within 12 mo, a distinct OC redistribution from c oarse into fine fractions was found with both dispersion methods. The accum ulation of OC was more pronounced for the size separates obtained by ultras onication, where the carbon distribution between 0.45- to 20-mum particle s ize fractions increased from 30% at the beginning to 71% at the end of the experiment. Dissolved organic carbon contents ranged between 50 and 68 g kg (-1) OC and decreased during the incubation. In conclusion, the exponential decrease of carbon mineralization and the OC enrichment in the fine partic le size fractions both indicated a distinct OM stabilization in the mining soil.