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.

This study investigated the carbon footprint of two different biochar production systems for application to paddy fields. The impacts of using rice straw-derived biochar in raw form (System A) were compared with those arising from using rice straw biochar enriched with lime, clay, ash and manure (System B). The GHG abatement of the management of one Mg of rice straw in Systems A and B was estimated at 0.27 and 0.61 Mg CO₂-eq, respectively, in spring season, and 0.30 and 1.22 Mg CO₂-eq in summer. The difference is mainly due to greater reduction of soil CH₄ emissions by enriched biochar.

This study presents a comparative analysis of the environmental impacts of different biochar-compost (COMBI) systems in North Vietnam relative to the conventional practice of open burning of rice husks. Three COMBI systems, using different pyrolysis technologies (pyrolytic cook-stove, brick kiln and the BigChar 2200 unit) for conversion of rice husk into biochar were modelled. Biochar was assumed to be composted with manure and straw, and the biochar-compost produced from each system was assumed to be applied to paddy rice fields. Life Cycle Assessment (LCA) showed that the three COMBI systems significantly improved environmental and health impacts of rice husk management in spring and summer compared with open burning, in terms of climate change, particulate matter (PM) and human toxicity (HT) impacts. The differences between the three COMBI systems in the climate change and PM impacts were not significant, possibly due to the large uncertainties. In all systems, the suppression of soil CH4 emissions is the major contributor to the reduced climate effect for the COMBI systems, comprising 56% in spring and 40% in summer. The greatest reduction in the HT impact was offered by the BigChar 2200 system, where biochar is produced in a large-scale plant in which pyrolysis gases are used to generate heat rather than released into the atmosphere.

Biochar can have a positive effect on agricultural soils and plant yields. The underlying mechanisms that deliver beneficial outcomes are still poorly understood. Soils contain complex communities of hundreds or thousands of distinct microorganisms, and it has been shown that biochar can have an impact on their composition and function. Here we analyse the microbial communities in a controlled field trial that compared the effect of enhanced biochars (EBs) against a farmer practice (FP) of traditional fertilisation (urea, superphosphate and potash) on sweet corn yield. During sequential crop cycles (barley and sweet corn) two types of EBs were applied at low and high levels (total of 1.1 and 5.44 t ha−1, respectively). Samples were taken at the end of a second crop cycle and over 50,000 16S ribosomal RNA (16S rRNA) tag sequences were generated per sample to characterise microbial communities. Despite the lower amounts of nutrients provided by EBs, their amendment to soil produced similar crop yields to the FP. In addition, significant differences in microbial community composition were observed between the high EB and FP treatments. This was driven by differences in the relative abundances of only a few community members. Community level differences were also correlated with a higher soil pH associated with EB laden soil. Network analysis showed that the low EB application had more correlation patterns (co-occurrences and exclusions) between microbial taxa, and highlighted the importance of associations between members of the phyla Acidobacteria and Verrucomicrobia in the biochar environment. Overall, a large number of microorganisms appear to be influenced by EB amendment compared with fertiliser use leading to a complex re-wiring of community composition and associations.