Use of Biochar From the Pyrolysis of Woody and Herbaceous Organic Matter as Soil Amendments.

Biochar is being promoted for its potential to improve soil properties, fertility and carbon sequestration in soil.  How this material might impact agricultural soils within temperate regions is largely unknown, Validation of biochar as a beneficial soil amendment and carbon sink would add important economic value to the pyrolysis process and spur adoption. Bio-chars from five waste feedstocks (pine chips, softwood bark, grass seed straw, peanut hulls, anaerobic digested manure fiber were produced with a pyrolysis unit developed by Washington State University. We evaluated each for their influence on the soil properties; pH, buffering capacity, cation exchange capacity, water retention curves, soil nutrient availability (N, P, K, S, micronutrients) soil biological activity, and C sequestration potentials of five soil types. Activated charcoal was included as a standard analysis and compared to biochars.            Herbaceous feedstock sources such as switchgrass and anaerobic digested manure had C contents of 60 and 67% respectively, as well as significantly higher N contents then the other biochars. Woody feedstocks: bark, soft bark and pine pellets had C contents above 75% with C:N ratios ranging from 176 - 588. Soil pH was found to increase 1 unit for the highest rate (1.5%) of biochar addition for the herbaceous feedstocks and 0.5-1.0 units for the woody sources. . Carbon sequestration potentials of each biochar and soil application rate were determined by long-term laboratory incubations.  Mineralization among biochars was significantly different only in the initial days of the incubation and can be partly explained by the presence of the hydrolysable C in the biochars. The increase in CO₂ evolved was 1-10 mg CO₂-C / g soil. The herbaceous materials (switchgrass and digested fiber) contained 5-6% hydrolysable C and < 0.2% N which may help explain the initial flush of CO₂ for these materials during the initial stages of mineralization.