Does size matter? An investigation into the impact of coarse and fine ground inoculated biochar on Hordeum vulgare (barley) growth and yield.

Biochar has historically demonstrated significant increases in plant growth through stimulation of the soil ecosystem, showing great potential as an economic and cost effective soil improvement method. In attempts to beneficially impact the soil microbiota, biochar of two different particle sizes were inoculated with plant growth promoting bacteria and introduced into the rhizosphere soil of barley. Control and experimental pots of barley were grown and monitored in a greenhouse for 9 weeks prior to harvest and analysis of growth traits. In general, yields of barley improved by at least 54% when coarse biochar was inoculated with bacteria (p = 0.113), compared to uninoculated coarse biochar or no biochar controls. In contrast, fine biochar performed significantly better without a microbial partner (p = 0.028). Significant changes in soil pH were detected (p = 0.020–0.068) in some of the treatments correlating with the different pH levels of the respective biochars. While both the fine biochar and the Fictibacillus-inoculated coarse biochar gave similarly large increases in fruit:shoot ratios in the barley, it was noted that the fine biochar is more difficult to handle and can pose an inhalation hazard when dry. Future work will focus on optimizing inoculated coarse biochar formulations for barley growth in open fields.