Abstract
Although thiamethoxam is an insecticide widely used in agriculture, its high mobility and persistence in the soil can result in contamination of groundwater and alteration in biogeochemical cycles. The objective of this study was to verify the effect of biochar, NPK fertilizer and thiamethoxam insecticide on soil microbial properties. The experiment was conducted in a randomized block design composed of the doses combination of mineral fertilizer NPK (0 and 300 kg ha-1 of the formulated 05-25-15), and biochar (0, 8, 16 and 32 t ha-1) in the absence and presence of thiamethoxam. Deformed soil samples were collected in all plots in the 0 to 0.10 m layer to determine the activity of the enzymes: acid and alkaline phosphatase, beta glucosidase and urease, beyond the microbial biomass carbon (MBC), basal respiration rate (C-CO2) and metabolic quotient (qCO2). To compare soil microbiology before and after the application of thiamethoxam, multivariate statistical techniques were used. The application of biochar resulted in increased enzymatic activity of urease, acid phosphatase, increase of qCO2 and basal respiration and reduction of MBC. In contrast, the application of the thiamethoxam insecticide suppressed the enzymatic activity of urease, acid phosphatase, resulting, however, in the elevation of alkaline phosphatase and basal respiration of the soil. Biochar application at doses greater than or equal to 16 t ha-1 resulted in elevation of qCO2 and reduction of MBC, regardless of the absence or presence of NPK chemical fertilization. Biochar effect on soil microbiological attributes is less significant than the effect of thiamethoxam application.
Highlights
Thiamethoxam insecticide is used worldwide in agriculture for the control of a wide variety of insect pests (Hilton, Jarvisa, & Ricketts, 2015)
Studies confirm the deleterious effect of thiamethoxam on the soil microbiota, such as toxicity to bacteria involved in the nitrogen cycle (Filimon et al, 2015), reduction in the activity of the urease, phosphatase and β-glucosidase enzymes (Jyot, Mandal, & Singh, 2015) and reduction of microbial biomass carbon (MBC) and basal soil respiration (Portillo, Scorza Junior Salton, Mendes, & Merchant, 2015)
The accesses grouped in clusters 1 and 2 represent the soil without the application of thiamethoxam insecticide, it is verified that the biochar doses of 16 and 32 t ha-1 modified the microbiological attributes of the soil when compared with the doses of 0 and 8 t ha-1
Summary
Thiamethoxam insecticide is used worldwide in agriculture for the control of a wide variety of insect pests (Hilton, Jarvisa, & Ricketts, 2015). The high demand for the use of this molecule in agricultural systems requires greater attention regarding its effects on the soil microbiota This concern elapses from the physico-chemical characteristics of thiamethoxam (low sorption interaction, high solubility), which gives it, above all, high soil persistence (Hladik, Kolpin, & Kuivila, 2014). The biochar presents high molecular stability, after its application to the soil, processes of oxidation of the aromatic structures forming new electric charges and reactive functional clusters in the soil occur (Petter et al, 2017) This higher reactivity may represent an improvement in the retention of molecules as it occurs in organic matter (Schmidt et al, 2015)
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