Effect of biochar addition on the behavior of the allelochemical S-carvone in agricultural soils

Abstract

Biochar (BC) has been proposed as a soil amendment due to its environmental and agronomic benefits once added to soils, playing an important role in sustainable waste management and circular economy. Additionally, the excellent sorbent properties of BC have led to intended use to enhance the persistence of allelochemicals in agricultural soils, in the context of their potential application as ecofriendly alternatives to synthetic pesticides. Allelochemicals have shown very short half lives in soils, which become the main constraint for their widespread use as green agrochemicals. Accordingly, sustainable strategies to enhance their soil persistence are encouraged (Galán-Pérez et al., 2022). This study aimed to characterize the changes in sorption and persistence of the allelochemical monoterpene S-carvone in two agricultural soils, one acidic and one alkaline, after their amendment with BC produced from composted olive mill waste at a pyrolysis temperature of 400 ºC. S-carvone was selected for being a representative of one of the most important families of allelochemicals, monoterpenes, and it is currently registered as a plant growth regulator. An additional novel approach of this work was to assess how the soil microbial activity of the soils was affected by the addition of BC and S-carvone through dehydrogenase enzymatic activity (DHA) and soil respiration measurements. The conditions used in the experiments were: rate of BC of 4%, soil humidity of 30%, and S-carvone application doses of 2 and 50 mg kg⁻¹. The sorption of S-carvone was greater in the acidic soil (31%) as compared to the alkaline soil (12%). After the addition of BC, the sorption of the allelochemical significantly increased in both soils, but the effect was more pronounced after its addition to the alkaline soil. The persistence of S-carvone in the BC-amended soils was also greater as compared to the unamended soils at the two application rates tested. The soil respiration and the DHA measurements demonstrated that BC had a positive effect on the microbial activity since higher values for the two parameters were measured for the BC-amended soils in comparison to the unamended soils. The results from this study suggest the effectiveness of BC in increasing the sorption and persistence of S-carvone and demonstrate that BC could contribute to modulating the behavior of allelochemicals in agricultural soils. Further studies relative to the analysis of the biodiversity of the unamended and BC-amended soil by DNA techniques are ongoing, which will help to gain a better knowledge of the effect of BC and allelochemicals on the soil microbial diversity and viceversa References Galán-Pérez, J. A. et al. (2022) Soil modification with organic amendments and organo-clays: Effects on sorption, degradation, and bioactivity of the allelochemical scopoletin, Journal of Environmental Management, 302, 114102. https://doi.org/10.1016/j.jenvman.2021.114102.