Different Effects of Ash Application on the Carbon Mineralization and Microbial Biomass Carbon of Reclaimed Mining Soils

Abstract

Ash resulting from biomass energy resource utilization contains a wide range of metal oxides and hydroxides, which may influence the capacity of the ash to be used as a soil amelioration material. This study aimed to assess the effects of different ashes on changes in soil carbon (C) mineralization and soil microbial biomass carbon (MBC) in reclaimed mining soils (RMSs). Different levels (0, 25, 50, and 75 Mg ha−1) of three ashes (rice husk, oil palm shell, and coal fly ash) were applied to 10-year RMS for a 120-day incubation period. Carbon mineralization was measured over the 120-day incubation period, while MBC and selected chemical properties were quantified at the end of the incubation period. The results of the study showed that the application of rice husk and oil palm shell ash at all levels and coal fly ash at low levels (≤ 25 Mg ha−1) increased C mineralization and MBC. However, the C mineralization and MBC of the soil decreased significantly when the amount of added coal fly ash reached 75 Mg ha−1. These decreases in C mineralization and MBC may be ascribed to the harmful effect of high amounts of coal fly ash on microbial activity and the increased specific surface areas and contents of Ca, Mg, oxalate- and dithionite-extractable iron and aluminum in soil with high amounts of added coal fly ash. This study demonstrates that the application of different types of ash to RMS leads to different C mineralization and soil MBC responses.