Carbon fractionation in a mine soil amended with compost and biochar and vegetated with Brassica juncea L

Abstract

The aim of this study was to evaluate the effect of the application of compost and biochar as soil amendments and planting of Brassica juncea L. to improve soil carbon fractions in a copper mine soil. A greenhouse experiment was carried out for 3months amending the mine soil with increasing proportions of compost and biochar mixture (20, 40, 80 and 100%) and planting Brassica juncea L. The results showed that the addition of amendments increased soil pH from 2.7 to 8.66, TC from undetectable levels to 149gkg−1, SOC from undetectable levels to 128gkg−1 and TN from undetectable levels to 11.13gkg−1. Organic amending also increased DOC (dissolved organic carbon) from undetectable levels to 25.56gkg−1, FOM (carbon in the free organic matter) from undetectable levels to 38.04gkg−1, FAP (carbon in fulvic acids removed with phosphoric acid) from undetectable levels to 15.57gkg−1, as well as increased the humification ratio, the humification index, the polymerisation rate and the organic carbon in the humified fractions (humic acids, fulvic acids and humin). Soils amended and vegetated with Brassica juncea showed lower values for FOM and FAP and higher values for humification ratio and polymerisation rate than the amended not-vegetated soils. Therefore, the combination of compost and biochar as soil amendment can be considered an efficient treatment to improve soil carbon fractions, making it suitable for a field scale application.