Use of biochar and oxidized lignite for reconstructing functioning agronomic topsoil: Effects on soil properties in a greenhouse study

Bekele, A., Roy, J. L. and Young, M. A. 2015. Use of biochar and oxidized lignite for reconstructing functioning agronomic topsoil: Effects on soil properties in a greenhouse study. Can. J. Soil Sci. 95: 269–285. Interest in the use of biochar as soil amendment has grown recently. However, studies evaluating its potential use for reclamation of disturbed agricultural lands are lacking. We studied the effects of amending clay, loam, and sand subsoil substrates with wood biochar pyrolized at 800°C, oxidized lignite (humalite), or labile organic mix (sawdust, wheat straw, and alfalfa; LOM) on soil organic carbon (C), microbial biomass, dry aggregated size distribution and penetration resistance in greenhouse. We also considered the co-application of LOM and biochar or humalite to the subsoil substrates as treatments where C from either biochar or humalite represented a stable form of C. The amount and composition of the mix of organic amendments was determined for each subsoil so that organic C levels of reconstructed topsoil would be equivalent to that of the corresponding native topsoil in the long term. Field pea (Pisum sativum L.) and barley (Hordeum vulgare L.) were grown in rotation in four sequential greenhouse studies. Results from soil analysis at the end of study II and study IV showed that subsoils amended with biochar or humalite had higher organic C than those with LOM only, regardless of soil type. Labile organic mix added alone or together with biochar or humalite to subsoil increased microbial biomass and decreased geometric mean diameter of the dry soil aggregates. The effects of biochar or humalite-only amendment on these soil properties were not significant relative to the unamended subsoil substrate. Simultaneous application of biochar or humalite with LOM can potentially be used for topsoil reconstruction and reclamation of disturbed agricultural lands, and to maintain soil quality in the long term. However, long-term field studies are required to ascertain the longevity of the desirable properties reported in this study and to assess effects associated with aging of biochar or humalite in the soil.