Potential of cattle manure pyrolysis liquid as an alternative environmentally friendly source of agricultural fungicides

Abstract The in vitro antifungal activity of the liquid fraction obtained from cattle manure pyrolysis was determined. Bio-oils and aqueous phases produced at 400, 500, and 600 °C were tested against two phytopathogenic fungi by incorporating the oil and water phase materials into culture medium, at concentrations of 1, 2, 3, 4, and 5 mg mL-1. The antifungal potentials were determined using colony growth diameters, as compared to controls. The aqueous phase produced at 400 °C and used at a concentration of 4 mg mL-1 provided 100% inhibition of mycelial growth and was fungicidal against both Lasiodiplodia theobromae and Fusarium solani. The bio-oils produced at all the different temperatures showed fungistatic potential, but there were no statistically significant differences among the products obtained at different temperatures, in terms of their inhibitory activities. Characterization by gas chromatography/mass spectrometry (GC/MS) and ultra-high resolution mass spectrometry (FT-Orbitrap MS) revealed that the materials were composed mainly of classes of oxygenated compounds. The GC/MS analyses showed that phenolic compounds were the main constituents of the bio-oils, with the relative area for these compounds increasing at higher pyrolysis temperatures. The liquid-liquid extraction process did not enable characterization of the aqueous phase by GC/MS, although the FT-MS analyses showed significant differences among the products, with the phase produced at 400 °C mainly presenting classes of aromatic nitrogen compounds. This prospecting study demonstrated the potential of using bio-oils and the aqueous phases from cattle manure pyrolysis as alternative sources of agricultural fungicides.