Sorption, Volatilization, and Efficacy of the Fumigant 1,3-Dichloropropene in a Biochar-Amended Soil

Sorption of the soil fumigant, 1,3-dichloropropene (DCP), on cornstraw biochar (fast pyrolysis at 500°C; specific surface area [SSA] of 3.0 m2 g−1) was strongly nonlinear and significantly greater on a soil–1% biochar mixture (26 Mg biochar ha−1) than on soil alone. This resulted in substantial reductions in DCP concentrations in the vapor phase. However, concentration of the fumigant in the aqueous phase of the soil, where it is active against soil nematodes, was also significantly reduced due to strong sorption to the biochar. In the studied system, adequate nematode control was achieved at 13 and 26 Mg biochar ha−1and DCP of 94 and 187 L ha−1, respectively, where the fumigant manufacturers suggested dose range of DCP is 84 to 514 L ha−1. Biochars produced at relatively high temperatures (>600°C) with a high SSA have been shown to absorb organic chemicals more strongly by one or more orders of magnitude than those, like the biochar used herein, produced at lower temperatures with a low SSA. Calculations show that adequate nematode control would not have been obtained had the biochar absorbed only five times more DCP per given solution concentration. Thus it is evident that while nematode control was adequate in the specific studied system, soil amendment with biochar could adversely impact pest control, depending on the sorption strength of the particular biochar. This issue should be considered when determining desirable biochar physical and chemical characteristics for use in agronomic systems.