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Comparative sorption and leaching study of the herbicides fluometuron and MCPA in a soil amended with biochar and other sorbents

Cabrera, Alegria, Cox, Lucia, Spokas, Kurt A., Celis, Rafael, Hermosin, M. Carmen, Comejo, Juan, Koskinen, William C.
ARS USDA Submissions 2011
MCPA (herbicide), activated carbon, biochar, biomass, calcium, feedstocks, fluometuron, hardwood, hulls, leachates, leaching, macadamia nuts, montmorillonite, olive oil, olive pomace, particle size, pyrolysis, sawdust, soil, soil amendments, sorption, surface area
Biochar is the solid residual remaining after the thermo-chemical transformation of biomass and, because of its numerous properties; it has been proposed to be used as soil amendment. In this work, the effect of soil amendment with six biochars from different feedstocks, production, and post-production handling on sorption and leaching of fluometuron and 2-methyl-4-chlorophenoxyacetic acid (MCPA) was studied and compared to the effect of other sorbents, such as an activated carbon, a Ca rich Arizona montmorillonite modified with hexadecyltrimethylammonium organic cation (SAZ-HDTMA) and an agricultural organic residue from olive oil production (OOW). Soils were amended at 2% (w/w) with the sorbents and studies were performed following a batch equilibration procedure. Sorption of both herbicides increased in all amended soils, except in the soil amended with a biochar produced from macadamia nut shells at fast pyrolysis and 850 ºC, which resulted in decreased sorption. On the other hand, both fluometuron and MCPA were completely sorbed and not detected in the leachates of the soil amended with activated carbon. Higher sorption and lower leaching of the herbicides were observed in the soils amended with the biochars with higher surface areas and the organoclay. Higher biochar surface area was correlated with decreasing biochar particle size. Despite the increase in herbicide sorption in soils amended with two hardwood biochars (hardwood sawdust with fast pyrolysis at 500 ºC and slow pyrolysis of hardwood at 540 ºC), leaching of fluometuron and MCPA was enhanced with the addition of these biochars and by the addition of OOW, which slightly increased herbicide sorption, when compared to the unamended soils. Our results indicate that not all biochar amendments will increase sorption. Furthermore, the amount and composition of the OM content of the amendment can play an important role on sorption and leaching of the herbicides fluometuron and MCPA.