Effects of biochar amendment on sorption, dissipation, and uptake of fenamiphos and cadusafos nematicides in sandy soil

BACKGROUND: The application of biochar to soil is supposed to alter its adsorption/desorption potential toward pesticides, thereby affecting their bioavailability and efficacy. This is particularly relevant in the case of nematicides because these pesticides are directly applied to soil. RESULTS: Biochar was produced from date palm (PB) and eucalyptus (EB) waste at 450 degrees C and added at a rate of 1% to a sandy soil. The half-life (t(1/2)) of fenamiphos was increased from 2.7 to 18.3 and 18.6 days in PB- and EB-amended soils, respectively. By contrast, the half-life of cadusafos was unaffected. Freundlich K-f values increased from 1.22 and 0.39 (mu g(1-Nf) g(-1) mL(Nf)) to 4.49 and 6.84 in 1% PB-amended soil, and to 3.49 and 4.62 in 1% EB-amended soil for cadusafos and fenamiphos, respectively. Plant uptake of both nematicides in tomato seedlings was reduced by approximately 97% (cadusafos) and 85% (fenamiphos). Although nematicide efficacy against Meloidogyne incognita was not altered at the recommended dosage, it was negatively affected at a half-dose rate. Under these conditions, it decreased from 43.1% in unamended sandy soil to only 18.3% in 1% PB-amended soil. CONCLUSIONS: Biochar addition increased the sorption capacity of soil. This resulted in a decrease of nematicide bioavailability, together with a reduction of both the dissipation rate and uptake by tomato plants. (C) 2018 Society of Chemical Industry