Fate of the carvone enantiomers after the addition of biochar to an agricultural soil

Abstract

In this work we investigated how amending a sandy loam agricultural soil with biochar (BC) at a rate of 2% (w:w) affected the sorption dissipation and leaching processes of the two enantiomers of the monoterpene carvone (R-carvone and S-carvone). Sorption of carvone in unamended and amended soil was a non-enantioselective process and the addition of the amendment enhanced the sorption capacity of the soil for both enantiomers. In addition carvone enantiomers showed greater resistance to be desorbed in BC-amended soil than in unamended soil. Dissipation of carvone in the soil was microbial-mediated and enantioselective with S-carvone being degraded more quickly than R-carvone. Furthermore the addition of BC increased the persistence of both enantiomers in the soil. Leaching of R- and S-carvone through soil columns was scarce for unamended soil (< 7%) and null for BC-amended soil for which much of the applied R- and S-carvone remained in the (amended) top 0-5 cm soil layer. Total recoveries of both enantiomers were greater for BC-amended soil columns than for unamended soil columns indicating reduced degradation in BC-amended soil. Our findings show that addition of biochars could help increase the persistence of carvone enantiomers in the topsoil where they may exert biological functions.