Publication Summary

Organic Waste to Resources Research and Pilot Project Report. Biochar is a charcoal-like material produced by the thermochemical pyrolysis of biomass materials. It is being considered as a potentially significant means of storing carbon for long periods to mitigate greenhouse gases. Much of the interest comes from studies of Amazonian soils that appear to have been amended with biochar which led to significant improvements in soil quality and large increases in crop yields. These changes have persisted for hundreds, if not thousands, of years. What is not known is how long it takes for biochar to integrate with the soil and thus express its benefits.

However, biochar does represent a stable form of carbon in soils and thus provides an intriguing potential carbon storage strategy. In this study, biochars from several different feedstocks were evaluated for their characteristics and their fate in five different Washington State soils. Herbaceous feedstock sources such as switchgrass and digester fiber (from anaerobically digested dairy manure) had C contents of 60 and 67% respectively, as well as significantly higher N contents then the other biochars. Woody feedstock biochars had C contents above 75% with C:N ratios ranging from 176-588. Activated charcoal had a C and N content of 87% and 0.47%, respectively. Biochars tested in this project raised soil pH, but did not lead to consistent plant growth improvements. Soil nitrate levels were reduced with increasing biochar rate, perhaps due to ammonium adsorption by the biochar. All biochars on all soil types did increase soil C; the largest carbon impact was on the Quincy sand, the soil with the lowest organic matter content. Biochar C was stable in soil, and mean residence times are estimated to be in the hundreds of years. Also, the biochar did not accelerate loss of indigenous organic matter through the ‘priming effect.′

The Washington State Department of Ecology provided funding for this project through the Beyond Waste Organics Waste to Resources (OWR) project. These funds were provided in the 2007-2009 Washington State budget from the Waste Reduction Recycling and Litter Control Account. OWR project goals and objectives were developed by the Beyond Waste Organics team, and were approved by the Solid Waste and Financial Assistance Program. Funding was from the Waste Reduction Recycling and Litter Control Account. OWR project goals and objectives were developed by the Beyond Waste Organics team, and were approved by the Solid Waste and Financial Assistance Program.