ARS | Publication request: Effect of carbonaceous soil amendments on potential mobility of weak acid herbicides in soil

Submitted to: International Humic Substances Society Conference
Publication Type: Abstract Only
Publication Acceptance Date: May 13, 2012
Publication Date: September 10, 2012
Citation: Koskinen, W.C., Cabrera, A., Spokas, K.A., Cox, L., Rittenhouse, J.L., Rice, P.J. 2012. Effect of carbonaceous soil amendments on potential mobility of weak acid herbicides in soil. In: Xu, J., Wu, J., He, Y. (Eds.). Functions of Natural Organic Matter in Changing Environment. Zhejiang University Press: Hangzhou, China. International Humic Substances Society Conference. p. 281-283.

Technical Abstract: Use of carbonaceous amendments in soil has been proposed to decrease potential offsite transport of weak acid herbicides and metabolites by increasing their sorption to soil. The effects of organic olive mill waste, biochars from different feed stocks, and humic acid bound to clay on sorption of MCPA, aminocyclopyrachlor, or indaziflam-acid metabolite to soils with varying physical and chemical properties were determined. At natural agricultural pH soil levels, these chemicals are anionic and weakly sorbed to soils; sorption of the three weak acids on soil was in the order MCPA (Kf = 0.1) < aminocyclopyrachlor (Kf = 0.3) < indaziflam-acid (Kf = 1.6). Results indicate that not all carbonaceous amendments, including biochars, increase sorption, thereby decreasing the potential for offsite transport. The amount and composition of the organic amendment, along with pH of the system, affect sorption and potential offsite transport. For instance, depending on the feedstock of the biochar and the method of production, changes in sorption ranged from no effect, to a decrease by a factor of 3.3X, to an increase of 383X upon addition of amendment to soil. In contrast, activated charcoal increased sorption by >10,000X. While generalizations have been made that soil sorption of nonpolar, neutral, or weakly basic chemicals increases by the addition of different carbonaceous amendments, no such generalizations can be made for weak acids. More work on properties of these amendments, biochars in particular, and how they affect weak acid sorption is required.