Influence of biochar amendments on the sorption-desorption of aminocyclopyrachlor, bentazone and pyraclostrobin pesticides to an agricultural soil

Authors: CABRERA, ALEGRIA - University Of Sevilla; COX, LUCIA - University Of Sevilla; Spokas, Kurt; HERMOSIN, M - University Of Sevilla; CORNEJO, JUAN - University Of Sevilla; Koskinen, William

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2013
Publication Date: 10/18/2013
Publication URL: http://handle.nal.usda.gov/10113/59594
Citation: Cabrera, A., Cox, L., Spokas, K.A., Hermosin, M.C., Cornejo, J., Koskinen, W.C. 2013. Influence of biochar amendments on the sorption-desorption of aminocyclopyrachlor, bentazone and pyraclostrobin pesticides to an agricultural soil. Science of the Total Environment. 470-471:438-443.

Interpretive Summary: Biochar has been gaining attention, both in the public and scientific circles, as a means to combat climate change and at the same time improve soil fertility. However, there has been very little attention focused on the impact of biochar additions have on chemicals applied to agricultural fields, such as herbicides and fungicides. In this research, we looked at the effect that 5 different biochars had when added to a agricultural soil (silt loam) on the changes in the sorption behavior of 3 different chemicals (2 herbicides and 1 fungicide). The impact of biochar was dependent on the characteristics of the biochar, since all biochars are not equal in terms of their chemical and physical make-up. The sorption of the agrochemicals was impacted the most by biochar that has a high surface area and a low amount of dissolvable organic matter on the biochar. Biochar with high amounts of other organic compounds can decrease the sorption of agrochemicals compared to the original soils, due to the competition for sorption sites between the target agrochemical and biochar's other organic matter. Thereby, this research highlights that biochar amendments need to be selected based on the desired mode of action and not all biochar types are suitable for sorbing chemicals in the soil system. Additional research is needed to fully characterize the surface chemistry responsible for these effects. These findings could provide additional insight and direction in the focus of the benefits of biochar additions on agrochemical fate. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved biochars based on properties to minimize agrochemical transport and improve soil carbon management.

Technical Abstract: The many advantageous properties of biochar have led to the recent interest in the use of this carbonaceous material as a soil amendment. However, there are limited studies dealing with the effect of biochar on the behavior of pesticides applied to crops. The objective of this work was to study the effect of various biochars on the sorption of the herbicides aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropyl-4-pyrimidinacarboxylic acid), bentazone (3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide) and the fungicide pyraclostrobin (methyl 2-[1-(4-chlorophenyl) pyrazol-3-yloxymethil]-N-methoxycarbanilate) to a silt loam soil. Aminocyclopyrachlor and bentazone were almost completely sorbed by the soils amended with the biochars produced from wood pellets. However, lower sorption of the herbicides was observed in the soils amended with the biochar made from macadamia nut shells as compared to the unamended soil, which can be attributed to the interactions and competition of the dissolved organic carbon (DOC) of the biochar with the herbicides for the sorption sites. Our results showed that pyraclostrobin is highly adsorbed to soil, and the addition of biochars to soil did not further increase its sorption. Thus, addition of biochars to increase the retention of low mobility pesticides in soil appears to be not necessary. On the other hand, biochars with high surface areas and low DOC contents can increase the sorption of highly mobile pesticides in soil.