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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #325523
Title: Metolachlor sorption and degradation in soil amended with fresh and aged biochar

Author
item TRIGO, CARMEN - Consejo Superior De Investigaciones Cientificas (CSIC)
item Spokas, Kurt
item HALL, KATHLEEN - University Of Minnesota
item COX, LUCIA - Consejo Superior De Investigaciones Cientificas (CSIC)
item KOSKINEN, WILLIAM - University Of Minnesota

Submitted to: Trade Journal Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2016
Publication Date: 4/6/2016
Citation: Trigo, C., Spokas, K.A., Hall, K.E., Cox, L., Koskinen, W.C. 2016. Metolachlor sorption and degradation in soil amended with fresh and aged biochar. Journal of Agricultural and Food Chemistry. 64(16):3141-3149.

Interpretive Summary: The environmental risk of applied pesticides to soils is often assessed through sorption experiments to guide field management decisions. This is particular important when decided on various organic amendments to add to soil to reduce leaching and run-off risks. However, a large number of current studies only examine the fresh or non-aged amendment. In this study, we looked at the impact of field-weathering on biochar, since both the physical and chemical properties of biochar will impact the observed sorption trends. We examined a macadamia nut shell biochar that was recovered from field plots at 1, 2, and 5 year time periods. Changes in sorption/availability of a herbicide (metolachlor) increased with incubation time to a greater extent in amended soil as compared to unamended soils; the sorption coefficient did decrease as a function of the age of the biochar. These data show that transport models would not accurately predict the herbicide movement in soil if effects of aging or biochar amendments are not considered. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved models for assessing agrochemical leaching risks based on mechanistic processes, which should be utilized in developing improved assessments of the fate and transport of applied agrochemicals.

Technical Abstract: Addition of organic amendments such as biochar to soils can influence pesticide sorption-desorption processes, and in turn, pesticide availability and biodegradation. Availability is affected by both the physical and chemical properties of soils and pesticides, as well as soil-pesticide contact time, or aging. Changes in sorption/availability of metolachlor with aging in soil amended with three macademia nut shells biochars aged zero (BCmac-fr), 1 year (BCmac-1yr) and 2 years (BCmac-2yr) and two wood biochars aged zero (BCwood-fr) and 5 years (BCwood-5yr) was determined. Sorption coefficient (Kd) values increased with incubation time to a greater extent in amended soil as compared to unamended soils; Kd increased by 1.2X for the unamended soil, 2.0X for BCwood-fr, 1.4X for BCwood-5yr, 2.4X for BCmac-fr, 2.5X for BCmac-1yr, and 1.9X for BCmac-4yr. This increase was the result of a 15% decrease in the metolachlor extractable with CaCl2 solution with incubation time in soil as compared to a 50% decrease in amended soil. Differences could possibly be due to diffusion to less accessible or stronger binding sites with time, a faster rate of degradation (in solution and on labile sites) than desorption, or a combination of the two in the amended soils. These data show that transport models would over-predict depth of movement of metolachlor in soil if effects of aging or biochar amendments are not considered.