Aggregate stability in mine residues after reclamation with biochar

Resumen

This study aims to assess how the addition of biochar and marble waste to acidic mine residues affected aggregatestability (AS) and contributed to the improvement of soil texture. For this purpose, a lab incubation was carried outfor 90 days. Biochars derived from pig manure (PM), crop residues (CR) and municipal solid waste (MSW) wereadded to the soil at a rate of 20 g kg-1. The marble waste (MW) was added at a rate of 200 g kg-1, with the aimof increasing pH from 3 to 8 (pH of the native soils of the area). Biochars and MW were applied independentlyand combined. A control treatment was used without application of amendments. The evolution of AS wasperiodically monitored at 2, 4, 7, 15, 30 and 90 days by the method of artificial rainfall. Results showed, at theend of the incubation, that the addition of MW alone did not significantly increased AS with comparison to CT(30%). However, the biochar, alone or together with MW, significantly increased AS, the treatment receiving CRderived biochar being the one with the highest values (46%). Increments in AS were significant from the day 30of incubation. AS showed a significant correlation with the total organic carbon content, but was not correlatedwith organic carbon fractions (soluble, labile, recalcitrant), inorganic carbon, microbial biomass carbon, enzymeactivities, exchangeable fraction of heavy metals (As, Cd, Cu, Pb, Zn), pH, electrical conductivity nor greenhousegas emissions (NO2, CH4). Thus, the application of biochar (alone or in combination with MW as a source ofcalcium carbonate) significantly increased the formation of stable aggregates in former acidic mine residues,favoring the development of soil structure, essential to create a soil from residues. It seems that the total content oforganic carbon is directly controlling aggregation, rather than other labile organic sources. Moreover, pH, salinityor the presence of exchangeable metals did not seem to affect soil aggregation.