Effect of Pyroligneous Acid on the Microbial Community Composition and Plant Growth-Promoting Bacteria (PGPB) in Soils

Pyroligneous acid (PA) is often used in agriculture as a plant growth and yield enhancer. However, the influence of PA application on soil microorganisms is not often studied. Therefore, in this study, we investigated the effect of PA (0.01–5% w/w in soil) on the microbial diversity in two different soils. At the end of eight weeks of incubation, soil microbial community dynamics were determined by Illumina-MiSeq sequencing of 16S rRNA gene amplicons. The microbial composition differed between the lower (0.01% and 0.1%) and the higher (1% and 5%) concentration in both PA spiked soils. The lower concentration of PA resulted in higher microbial diversity and dehydrogenase activity (DHA) compared to the un-spiked control and the soil spiked with high PA concentrations. Interestingly, PA-induced plant growth-promoting bacterial (PGPB) genera include Bradyrhizobium, Azospirillum, Pseudomonas, Mesorhizobium, Rhizobium, Herbaspiriluum, Acetobacter, Beijerinckia, and Nitrosomonas at lower concentrations. Additionally, the PICRUSt functional analysis revealed the predominance of metabolism as the functional module’s primary component in both soils spiked with 0.01% and 0.1% PA. Overall, the results elucidated that PA application in soil at lower concentrations promoted soil DHA and microbial enrichment, particularly the PGPB genera, and thus have great implications for improving soil health.

Bioactivity of Neem Seed Oil mixed with Pyroligneous Acid from Rice Husks against Spodoptera litura

Biopesticides are environmentally friendly solutions used for pest control management. This is a feature of Neem (Azadirachta indica) seed oil and tar, which provides a synergistic effect on the bioactivity of pyroligneous acid, and both are known to have bioactive compounds. Therefore, the purpose of this study was to evaluate the effect of neem seed oil and tar on pyroligneous acid from rice husks in conventional emulsion form, and their efficacy on the polyphagous insect Spodoptera litura. Neem seed oil was added at concentrations of 10, 20, 30, and 40%, while the concentration of tar was 0.5, 1.0, and 2.0%. The conventional emulsion formed was then characterized using a digital microscope. The addition of neem seed oil and tar were able to increase the antifeedant activity of pyroligneous acid by 63.6 % while both neem oil and tar by 72.6 %. The 2.0% tar formulation (N4PT2) showed the highest antifeedant activity against S.litura (97.9 %) and had the smallest droplets size ranges (2.90 - 24.16 µm). The addition of tar tends to reduce the droplet size of neem oil and increase antifeedant activity.

Influence of Pyroligneous Acid on Fermentation Parameters, CO2 Production and Bacterial Communities of Rice Straw and Stylo Silage

Carbon dioxide (CO2) is a primary greenhouse gas and the main cause of global warming. Respiration from plant cells and microorganisms enables CO2 to be produced during ensiling, a method of moist forage preservation applied worldwide. However, limited information is available regarding CO2 emissions and mitigation during ensiling. Pyroligneous acid, a by-product of plant biomass pyrolysis, has a strong antibacterial capacity. To investigate CO2 production and the influence of pyroligneous acid, fresh stylo, and rice straw were ensiled with or without 1% or 2% pyroligneous acid. Dynamics of the fermentation characteristics, CO2 production, and bacterial communities during ensiling were analyzed. Pyroligneous acid increased the lactic acid content and decreased the weight losses, pH, ammonia-N content, butyric acid content, and coliform bacterial numbers (all P < 0.05). It also increased the relative abundance of Lactobacillus and decreased the relative abundances of harmful bacteria such as Enterobacter and Lachnoclostridium. Adding pyrolytic acids reduced the gas production, especially of CO2. It also increased the relative abundances of CO2-producing bacterial genera and of genera with the potential for CO2 fixation. In conclusion, adding pyroligneous acid improved the fermentation quality of the two silages. During ensiling, CO2 production was correlated with bacterial community alterations. Using pyroligneous acid altered the bacterial community to reduce CO2 production during ensiling. Given the large production and demand for silage worldwide, application of pyroligneous acid may be an effective method of mitigating global warming via CO2 emissions.

Effect of Pyrolysis Temperature on the Characterisation of Dissolved Organic Matter from Pyroligneous Acid

Dissolved organic matter (DOM) greatly influences the transformation of nutrients and pollutants in the environment. To investigate the effects of pyrolysis temperatures on the composition and evolution of pyroligneous acid (PA)-derived DOM, DOM solutions extracted from a series of PA derived from eucalyptus at five pyrolysis temperature ranges (240–420 °C) were analysed with Fourier transform infrared spectroscopy, gas chromatography–mass spectroscopy, and fluorescence spectroscopy. Results showed that the dissolved organic carbon content sharply increased (p < 0.05) with an increase in pyrolysis temperature. Analysis of the dissolved organic matter composition showed that humic-acid-like substances (71.34–100%) dominated and other fluorescent components (i.e., fulvic-acid-like, soluble microbial by-products, and proteinlike substances) disappeared at high temperatures (>370 °C). The results of two-dimensional correlation spectroscopic analysis suggested that with increasing pyrolysis temperatures, the humic-acid-like substances became more sensitive than other fluorescent components. This study provides valuable information on the characteristic evolution of PA-derived DOM.