Changes in sorption and bioavailability of herbicides in soil amended with fresh and aged biochar

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

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2018
Publication Date: 3/1/2019
Citation: Gamiz, B., Velarde, P., Spokas, K.A., Celis, R., Cox, L. 2019. Changes in sorption and bioavailability of herbicides in soil amended with fresh and aged biochar. Geoderma. 337:341-349. https://doi.org/10.1016/j.geoderma.2018.09.033.
DOI: https://doi.org/10.1016/j.geoderma.2018.09.033

Interpretive Summary: This research examined the impact of soil aging of an oak hardwood biochar that was buried in a silt loam soil for 6 months in the Upper Midwest (Wisconsin). This aged biochar was compared to a fresh biochar (one that was not buried in the soil) to assess differences in sorption and degradation for three different pesticides. There was a significant difference observed in the amount of pesticide sorption as a function of aging, with the soil aged biochar sample sorbing higher amounts (>85%) of all pesticides in the laboratory experiments compared to the fresh biochar samples which sorbed less than 15%. Both biochar samples had similar chemistries, as assessed through spectroscopic and total elemental analyzes. The biochar aging did not show any oxidation or chemical alterations for the 6-month period. These results are significant to farmers and policy makers and will assist scientists and engineers in understanding the potential alteration in the sorption potential for biochar once it is applied to soils. These results show the variability of biochar sorption capacities and changes with time after its addition to soil, which will affect the long-term control of pests and environmental fate of applied pesticides.

Technical Abstract: Prediction of long-term pesticide behavior in soil amended with biochar (BC) is still contradictory. In this work, the sorption of three highly persistent and ionizable pesticides, two anionic (imazamox and picloram) and one weak base (terbuthylazine), on fresh and aged BC and on soil amended with the biochars was compared. Aging consistent in buried the biochar in a silt loam soil in Wisconsin (USA) during six months. Additionally, the implication of sorption in pesticide bioavailability was also assessed by means of soil incubation experiments. Aged BC sorbed the three pesticides in greater extent (> 85%) in comparison to the fresh BC. This was attributed to differences in the dissolved (organic or inorganic) components of the sorbent. Dissipation in soil was pesticide and biochar dependent. The amounts of soil extractable (bioavailable) pesticides were influenced by their sorption behavior during the incubation experiment. Imazamox did not adsorb to BC, neither fresh nor aged, and the sorption scarcely increased in both fresh and aged BC-amended soil. Conversely, both picloram and terbuthylazine were extracted in lower amounts in aged BC-amended soil as compared to unamended or to fresh BC-amended soil, showing faster dissipation at the beginning of the experiment. This was related to the higher sorption of these pesticides on aged BC-amended soil, which derived in rapid degradation or strong sorption (irreversible). Our work shows the variability of biochar sorption capacities and changes with time after its addition to soil, which will affect the bioefficacy and microbial availability of pesticides in the rhizosphere.