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Title: Biochar amendment to the soil surface reduces fumigant emissions and enhances soil microorganism recovery

Author
item SHEN, GUOQING - Shanghai Jiaotong University
item ASHWORTH, DANIEL - University Of California
item GAN, JIANYING - University Of California
item Yates, Scott

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2016
Publication Date: 1/4/2016
Citation: Shen, G., Ashworth, D.J., Gan, J., Yates, S.R. 2016. Biochar amendment to the soil surface reduces fumigant emissions and enhances soil microorganism recovery. Environmental Science and Technology. 50:1182-1189. doi: 10.1021/acs.est.5b03958.

Interpretive Summary: Soil fumigants are used to kill plant pests in soil and increase crop production. However, they are volatile, toxic and can negatively affect air quality; therefore, strategies are required to reduce their emissions into air. These strategies should not reduce the potential for killing pests, and, ideally, aid the recovery of beneficial soil microorganisms that are killed by the fumigant. Applying biochar (biomass that has been heated in a closed container with little, or no, air) to the soil surface may be a highly suitable strategy for achieving these goals. In cylindrical soil columns, we studied the soil-air emissions and distribution within the soil of two common fumigants, 1,3-dichloropropene (1,3-D) and chloropicrin (CP) after the addition of two types of biochar to the soil surface. We also investigated the recovery of soil microbes after the fumigation. Compared to previously used methods of reducing emissions (covering the soil with plastic tarp, and adding a chemical to increase the degradation of the fumigants) and a control (bare soil), biochar derived from rice husk was highly effective at reducing emissions of both fumigants from the soil to the air. Biochar derived from green waste was highly effective only for 1,3-D. For the biochar derived from rice husk, concentrations of both fumigants within the soil remained high relative to the other treatments, indicating that pests mat be controlled effectively. Moreover, when mixed with the soil after the fumigation, the biochar derived from rice husk resulted in a faster recovery of soil microorganisms compared to the other treatments. We conclude that certain types of biochar may, depending on their physical and chemical characteristics, be highly effective in reducing soil-air emissions of fumigants without compromising pest kill efficacy and recovery of soil microbes. This research would be of interest to scientists, regulators, cooperative extension personnel and grower groups.

Technical Abstract: 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. In the present study, replicated soil columns were used to study the effect of biochar derived from rice husk (BR) and green waste (BG) applied to the soil surface on 1,3-dichloropropene (1,3-D) and chloropicrin (CP) emissions and soil gas distribution, and on microorganism population re-establishment. Relative to the control, high density polyethylene (HDPE) and ammonium thiosulfate (ATS) treatments, BR gave the greatest reductions for both fumigants and had no obvious single emission peak, while BG was very effective only for 1, 3-D. The emission fluxes of 1,3-D were below 0.02 µg m-2s-1 for BR and 0.19 µg m-2s-1 for BG, and these are comparable to fluxes previously observed for virtually impermeable film (VIF) which is commonly regarded as the most effective emission reduction strategy for soil fumigants. With BR application, the concentration of fumigant in the soil gas was higher than in the control and ATS treatment. After the soil column experiment, mixing the BR with the fumigated soil resulted in higher soil respiration rates (a measure of microbial activity) than were observed for HDPE and ATS treatments. This study indicated that biochar amendment to the soil surface may be an effective strategy for fumigant emission reduction and the recovery of the soil microorganism population established post-application.