Biochar Application to Soil: Agronomic and Environmental Benefits and Unintended Consequences

Biochar is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation, and as a soil amendment. The published reviews on biochar application to soil have so far focused mainly on the agronomic benefits, and have paid little attention to the potential unintended effects. The purpose of this chapter is to provide a balanced perspective on the agronomic and environmental impacts of biochar amendment to soil. The chapter highlights the physical and chemical characteristics of biochar, which can impact on the sorption, hence efficacy and biodegradation, of pesticides. As a consequence, weed control in biochar-amended soils may prove more difficult as preemergent herbicides may be less effective. Since biochars are often prepared from a variety of feedstocks (including waste materials), the potential introduction of contaminants needs to be considered before land application. Metal contaminants, in particular, have been shown to impact on plant growth, and soil microbial and faunal communities. Biochar has also been shown to influence a range of soil chemical properties, and rapid changes to nutrient availability, pH, and electrical conductivity need to be carefully considered to avoid unintended consequences for productivity. This chapter highlights some key areas of research which need to be completed to ensure a safe and sustainable use of biochar. In particular, understanding characteristics of biochars to avoid ecotoxicological impacts, understanding the effects of biochar on nutrient and contaminant behavior and transport, the effects of aging and the influence of feedstock and pyrolysis conditions on key properties are some of the areas that require attention.