Comparison of the Physical and Chemical Properties of Laboratory- and Field-Aged Biochars.

In order to predict long-term impacts of biochar on soil properties and agronomic outcomes, it is necessary to better understand the aging of biochars in soil environments and the impact of aged biochars on soil physical, chemical, and biological processes. The goal of this study was to compare laboratory and 2-3 year old field aged biochars, specifically the changes in adsorption properties, elemental ratios, reactive and non-reactive C-dynamics, and other  physical and chemical properties. Three different biomass feedstocks each produced by two different pyrolysis techniques were subjected to a laboratory controlled chemical aging process. Fresh biochars were incubated for one month at 40°C in 1M HCl with periodic additions of 30% H₂O₂, washed with 1M CaCl₂ followed by de-ionized water, and then incubated for one month in the presence of dissolved organic carbon. Field aged coarse biochar particles were separated from biochar amended soils by wet sieving and hand picking. All relevant physicochemical parameters will be compared for all fresh, chemically, and field aged biochars. This simulated chemical aging process of biochars in the laboratory was expected to alter some physicochemical properties including cation exchange capacity, extent of humification, and surface acid functional groups of the feedstock materials. Percentage of reactive C would be expected to increase due to the chemical aging processes occurring, with important implications for C-sequestration potential. The resulting beneficial effects of the artificial chemical aging on biochar properties would be comparable to field-aged biochar in terms of soil properties and agronomic impacts, and for assessing C-sequestration potential. An ability to predict the long-term impacts of biochar amendments on soil properties and agronomic outcomes would facilitate the development of cropping systems models and the assessment of economic and environmental benefits on a global scale.