Buried woodchips or biochar as a means of soil productivity and carbon restoration: Effects on microbial activities, soil carbon cycling and plant cover in a semiarid ecosystem

Soil degradation is a global issue that is especially problematic in water-limited ecosystems that are vulnerable to desertification. Ongoing climate change promotes desertification in combination with expansive agriculture and rangelands, mining activities, and changing fire regimes that disturb plant succession patterns. Organic amendments, such as woodchips and biochar, are applied to re-establish vegetative cover and rooting systems in degraded soils, though they also influence the soil biological activities and soil carbon stocks and fluxes. The objective of this study was to assess how woodchips and biochar incorporated into the soil influence soil carbon dynamics, microbial activities, and revegetation of disturbed soils that differ in porosity and clay content. We hypothesized that adding amendments would create soil microenvironments enabling greater microbial activities and biomass growth compared to non-amended soils. Greater microbial activities will enhance nutrient cycling and soil carbon and therefore the soils capacity to support vegetation. Woodchip and biochar amendments should differ in the magnitude of microbial activity increase and the subsequent soil carbon gains because woody biochar is inherently more resistant to decomposition. Results from the first year of a long-term monitoring experiment show that neither the woodchips nor biochar influenced microbial exoenzyme activities or microbial biomass carbon. Incorporated woodchips did significantly reduce plant cover, but significantly increased dissolved organic carbon and soil efflux. We also found increasing soil efflux to correlate with increasing specific carbon and nitrogen exoenzyme activities. Soil type and sample date (soils sampled following the summer and winter monsoons) also significantly influenced microbial variables and responses. Our results of reduced plant cover and increased soil CO²efflux demonstrates that the burial of organic wood waste in a semiarid ecosystem may increase exoenzyme activities per unit biomass and soil carbon loss in the short term.