Changes produced during the stabilization of wheat straw based-compost and effects of compost application to copper contaminated soil

Abstract

In order to enhance carbon (C) stabilization of wheat straw-based compost and to analyze the effects of composts in copper (Cu) contaminated soils, the following studies were conducted. In a first stage, wheat straw-based composts were inoculated with Trametes versicolor, and co-composted with iron-aluminium (Fe-Al) oxides and clay minerals. In a second stage, to evaluate effects of compost in soil organic matter (SOM) and microbial activities, decomposition experiments by monitoring the release of CO2 were performed. Soil samples were mixed with compost and placed in respiration jars. The OM transformations occurred during composting and the effects of compost in SOM were observed by 13CNMR. Finally, Cu availability was evaluated by sequential fractionation. The CO2 release varied between treatments being higher in Tv compost-amended soil (~160 mg kg-1 CO2). Metallic oxides treated composts showed a lower respiration than no treated composts. Solid state 13C NMR spectra from composting showed differences regard the relative distribution highlighting an increase of aromatic C in composts treated with iron oxide. Signals obtained from soil-compost incubations spectra showed that un-amended soils showed broad signals, from the aliphatic (0-110 ppm), aromatic (110-160 ppm), and carboxylic (160-185 ppm) regions. In contrast, spectra from compost amended soils exhibited well-defined signals, especially those associated with lignin (148 and 154 ppm) and derived structures. Compost addition reduced the easily exchangeable fraction and increased organic-bound to Cu. Our results suggest that inorganic materials applied to wheat straw-based compost could promote its stabilization. The solid-state 13CNMR analyses allowed identifying changes in SOM by compost addition after one year. We concluded that the use of stabilized wheat straw based-composts in Cu contaminated soils can represent a potential technology to increase C stock and decrease the Cu availability.