Is current biochar research addressing global soil constraints for sustainable agriculture?

• Biochar soil experiments quantitatively assessed in terms of research interests and conditions.
• The experiments biased on less constrained soils, in laboratory and pot experiments.
• Biochars used more often from wood than crop residue, from lab prepared than engineered.
• Global-linked studies should be developed for upscaling of biochar use in world agriculture.

Soil degradation is an increasing threat to the sustainability of agriculture worldwide. Use of biochar from bio-wastes has been proposed as an option for improving soil fertility, degraded land restoration, and mitigating the greenhouse gas emissions associated with agriculture. Over the past 10 years, there have been hundreds of research studies on biochar from which it may be possible to determine appropriate methods for use of biochar to improve sustainable agriculture. To address potential gaps in our understanding of the role of biochar in agriculture, in this paper are reviewed the studies of 798 publications of field-, greenhouse- and laboratory-based biochar amendment soil experiments conducted as of August, 2015. Here we report the findings from a quantitative assessment. The majority of published studies have been performed in developed countries in soils that are less impaired than those found in many developing countries. The majority of the works involves laboratory and greenhouse pot experiments rather than field studies. Most published studies on biochar have used small kiln or lab prepared biochars rather than commercial scale biochars. And, most studies utilize wood and municipal waste feedstocks rather than crop residues though the later are often available in agriculture. Overall, the lack of well-designed long-term field studies using biochar produced in commercial processes, may be limiting our current understanding of biochar’s potential to enhance crop production and mitigate climate change. We further recommend greater alliance between researchers and biochar production facilities to foster the uptake of this important technology at a global scale.