Effect of Biochar Amendments on Microbial Transport through Soils.

The incorporation of biochar into soils had been shown to improve soil fertility, enhance soil sequestration of carbon and decrease the mobility of agrochemicals and heavy metals. Our series of column experiments have shown that in addition to these benefits, biochar amendments can limit bacterial transport through soil. We investigated the role of biochar feedstock type (poultry litter and pine chips), biochar pyrolysis temperature (350 and 700 ^oC), biochar application rate (1, 2, and 10%), soil moisture content (saturated and 50% saturation), soil texture (1 and 12 % clay content), and bacterial surface properties on microbial transport through biochar-amended soils. Biochar amendments significantly reduced bacterial transport in most cases and were shown more effective when biochars pyrolyzed at higher temperatures are soil-amended at higher application rates. In general, pine chip biochars were much more effective than poultry litter biochars. We also found that bacterial retention in biochar-amended soils was observed to be more effective in partially saturated than in fully saturated conditions and that the benefit of biochar amendment in decreasing bacterial transport is more pronounced in soils with lower clay content.  Differences in surface properties of the bacteria were shown to affect their degree of retention in biochar amended soil. Our results suggest that utilization of biochars as amendment to reduce the transport of bacteria in soils is promising. However, we also found that interactions between biochar and bacteria are complicated and need further investigations to determine the mechanisms involved.