Biochar changes the bioavailability and bioefficacy of the allelochemical coumarin in agricultural soils

Authors: GAMIZ, BEATRIZ - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC); LOPEZ-CABEZA, ROCIO - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC); VELARDE, PILAR - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC); Spokas, Kurt; COX, LUCIA - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC)

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2020
Publication Date: 9/14/2020
Citation: Gamiz, B., Lopez-Cabeza, R., Velarde, P., Spokas, K.A., Cox, L. 2020. Biochar changes the bioavailability and bioefficacy of the allelochemical coumarin in agricultural soils. Pest Management Science. 77(2):834-843. https://doi.org/10.1002/ps.6086.
DOI: https://doi.org/10.1002/ps.6086

Interpretive Summary: For the first time, the fate of the allelochemical coumarin in unamended soil and soil amended with fresh and soil-aged biochar is reported. Biochar additions modified the soil’s retention capacity towards coumarin and consequently, changed its degradation and leaching patterns. The aging process did not alter the sorption capacity of biochar with respect to coumarin, likely, the increase in organic matter content was the dominant factor that controlled sorption of the compound instead of the surface chemistry alterations due to soil aging. There was no consistency between dissipation, leaching, and application rate, which reveals the problems relating dissipation and mobility of natural compounds in soils, since they are rapidly degraded. Biochar additions enhanced coumarin activity only at high application rates. These results are significant to assist scientists, engineers, and farmers, and supply guidance for the use of biochar amendments as a promising tool to enhance the activity of allelochemicals.

Technical Abstract: Aim: Allelochemicals can act as pesticides or enhance the action of synthetic pesticides. In this work, we assessed the bioavailability of the allelochemical coumarin in soils amended with fresh or field-aged biochars. Methods: The fresh biochar from oak wood (Fresh BC) was prepared at 550 ºC and was buried for aging in two different places: in a sandy loam soil in Spain for 15 months (Aged BC_1) as well as a sandy loam soil in USA for 6 months (Aged BC_2). To assess the bioavailability of coumarin, sorption, dissipation, leaching and bioefficacy experiments were conducted in unamended soil and soil amended with fresh and aged biochars. Results: Sorption experiments showed that all biochars were able to increase the affinity of soil towards coumarin; although, no statically significant differences were observed between treatments. All biochars ensure greater persistence of coumarin and the effect was more pronounced at high chemical dose (10 mg/kg). Conversely, leaching studies in soil columns revealed that biochars were able to maintain coumarin within the first 5 cm of top-soil and leaching was only observed when coumarin was added at the highest rate (10 kg/ha). Similarly, the bioefficacy of coumarin against lettuce was enhanced only at 10 kg/ha with biochar amended soil. Conclusions: Biochar application to agricultural soils is a promising tool for the management of natural compounds with potential use as biopesticides such as coumarin, since it increases sorption, persistence and, in some cases, bioefficacy. Results from this study reveal that this effect still persists with aging of biochar in soils.