Assessing the effect of organoclays and biochar on the fate of abscisic acid in soil

Authors: GAMIZ, BEATRIZ - Collaborator; COX, LUCIA - Collaborator; HERMOSIN, M. CARMEN - Collaborator; Spokas, Kurt; CELIS, RAFAEL - Collaborator

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2016
Publication Date: 1/11/2017
Citation: Gamiz, B., Cox, L., Hermosin, M., Spokas, K.A., Celis, R. 2017. Assessing the effect of organoclays and biochar on the fate of abscisic acid in soil. Journal of Agricultural and Food Chemistry. 65(1):29-38. doi:10.1021/acs.jafc.6b03668.

Interpretive Summary: The environmental risk of applied pesticides to soils is often assessed through sorption experiments to guide field management decisions. However, very little attention has been focused on the different chemical structures or optical isomers that exist with some compounds. These structure differences can control their fate in the soil system. In this study, we looked at the impact of three different amendments (organoclays and a biochar) on the overall impact on the sorption and degradation of two optical isomers of the plant hormone abscisic acid (ABA). There were differences between the three amendments in the sorption and overall transport of ABA through the soil system. These data show that different soil amendments could impact the distribution in the optical isomers and this can alter the distribution of the isomers remaining in the soil system. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved models for assessing agrochemical fate and effectiveness based on mechanistic processes accounting for the optical isomers of some compounds, which should be utilized in developing improved assessments of the fate and transport of applied agrochemicals.

Technical Abstract: The potential use of biopesticides in agriculture is a subject of increasing interest. Addition of certain amendments to agricultural soils can influence the presence as well as the selectivity of chemical optical isomers in soils, but for biopesticides this is still an unexplored area. In this work, sorption-desorption isotherms of racemic abscisic acid (ABA) on two organoclays [SA-HDTMA and Cloisite10A (Cloi10)] and on biochar from apple wood (BC) were obtained. The study was completed with an incubation and leaching experiment after the addition of these sorbents to an agricultural soil at a rate of 2% (w/w). Higher affinity towards ABA was displayed by SA-HDTMA followed by Cloi10 and BC, and non-enantioselective processes were observed. Desorption could be ascertained only in BC, where ABA enantiomers presented difficulties to be desorbed. On the other hand, dissipation was always enantioselective with S-ABA being degraded faster than R-ABA, and followed the order: unamended > Cloi10-amended > BC-amended > SA-HDTMA-amended soil for both enantiomers. Sorption determined along the incubation experiment indicated some loss of sorption capacity with time in organoclay-amended soil and increasing sorption in BC-amended soil, suggesting superficial sorption for organoclays and slow (potentially diffusion controlled?) sorption kinetics in BC-amended soil. The leaching of both R-ABA and S-ABA was delayed after amending soil to an extent that depended on the amendment sorption capacity, and it was almost suppressed by addition of BC due to its irreversible sorption. Our findings show that addition of organoclays and BC differently affected the final behavior and enantioselectivity of ABA in soil as a consequence of dissimilar sorption capacities and alterations in sorption with time. These amendments could therefore impact the fate of endogenous and exogenous ABA in soils, particularly with regard to its plant and microbial availability in the rhizosphere.