Biochar Amendment to the Soil Surface Reduces Fumigant Emissions and Enhances Soil Microorganism Recovery.

During soil fumigation, it is ideal to mitigate soil fumigant emissions, ensure  pest control efficacy, and speed up the recovery of the soil microorganism population established post-application. However, there is currently no fumigant emission reduction strategy that can meet all the above requirements. Biochar potentially offers a significant opportunity of achieving these goals. We used 1,3-dichloropropene (1,3-D) and chloropicrin (CP) as representative soil fumigants to research the effect of biochar amendment to the soil surface on fumigant emissions, soil gas distribution and microorganism population re-establishment in replicated soil columns. The results showed that biochar applied with ammonium thisolfate (ATS), delayed markedly the release of fumigants from the soil relative to high density polyethylene (HDPE) and ATS-only treatments. The maximum emission rate for ATS-only and HDPE treatments occurred about 24h after fumigation and for the control after 16h, however, with biochar treatment it occurred after 300h. The decreasing order of the emission rates maxima was as follows: Control >HDPE>ATS>Biochar+ATS  for 1,3-D  and Control >HDPE>ATS>Biochar+ATS for CP. Therefore, Biochar was most effective at reducing emission rates.  Compared with virtually impermeable film (VIF), the maximum emission rate from the biochar treatment was lower for 1,3-D and only slight higher for CP. With biochar amendment, the distribution of fumigant over time in the soil-gas phase was similar to the ATS-only treatment. The concentration of fumigant in soil was higher than in the control, slightly higher than in the ATS treatment, and lower than under HDPE during 2 days of fumigation. As some studies have shown that ATS-only did not adversely impact on fumigation efficacy, therefore, this suggests that biochar amendment would not result in reduced fumigation efficacy.  Soil respiration in the soil after 14 days of fumigation showed that the recovery rate of soil microorganisms when mixing biochar with fumigated soil was higher than in the HDPE and ATS-only treatments. The primary result suggests that the fumigant emission reduction by biochar may be attributable to the special structure of biochar (sorption sites and electron conductors) which absorb and catalyze the reduction of the fumigant.