Recycling of Biochar as a Co-product of Pyrolysis: pH and Microbial Effects.

Globally escalating demands for food and bioenergy have raised concerns about the potential for agricultural biofuels to be sustainable, abundant and environmentally-beneficial energy sources. The production of sustainable bioenergy requires a comprehensive understanding for the appropriate use of co-products to maintain balanced carbon cycling. The objective of this work was to determine the impact of selected unwashed gasification ash and pyrolysis biochars on soil pH and carbon dioxide (CO2) emissions from three different soils: Cecil from Georgia, Barnes eroded and Barnes non-eroded from Minnesota. Char/ash material was obtained from various feedstocks that included turkey manure plus wood chips, peanut hulls, pine woodchips and two types of corn stover. These materials were applied at the rate of 25.8 g biochar per kilogram of soil (estimated to be 10 times the carbon in one crop of corn stover) and water was added to bring the soil to field capacity. A sample of weathered biochar made from peanut hulls was also used. The pH of the char in water ranged from 7.6 for the weathered char to 10.6 for the turkey manure ash. The soil pH in a 2:1 suspension was 6.3, 8.4, and 8.3 for the Cecil, Barnes eroded and Barnes non eroded, respectively. The soil pH with the added biochar/ash increased in every case. The addition of biochar to the soil generally decreased the CO2 emissions relative to the soil only with the largest decrease on the Cecil soil. Ongoing studies are evaluating biochar properties as influenced by addition of nitrogen and sugar solutions. This preliminary laboratory study suggests the need for further laboratory and field research for a better understanding of bio-char material and its ability to maintain soil quality.