The synergistic effect of sewage sludge biochar and Trichoderma harzianum on soybean yield

The use of sewage sludge to produce biochar is one of the best alternatives for the final destination of this material, allowing for reuse of nutrients and reducing the dependence on mineral fertilizers. Sewage sludge biochar (SSB) stands out as an enhancer of the physical, chemical and biological properties of the soil. The use of beneficial microorganisms such as 'Trichoderma' spp. in combination with biochar may have a synergistic effect on the development of different plants and needs to be better studied. The SSB was produced from sewage sludge biomass (SS) obtained from the sewage treatment plant (STP) of the Federal District Environmental Sanitation Company (CAESB), Brasilia, DF, Brazil. The SSB was produced in an electric tubular furnace at 500 degreesC and showed the following characteristics: carbon (19%), nitrogen (2.3%), hydrogen (1.7%), specific surface area (52.5 m2 g-1), pore volume (0.053 ml g-1). An experiment was carried out in a greenhouse to evaluate the synergistic effect of SSB application (0.5% w/w) in combination with 'T. harzianum' (TH) on soybean development. The treatments adopted were: (1) control - autoclaved soil, (2) TH, (3) SSB and (4) SSB + TH. The SSB was applied 15 days before soybean planting and the TH was applied to the soil two times, once at eight days before planting and the other at the time of planting. The SSB resulted in a 200% increase in the number of pods when compared to the exclusive application of 'T. harzianum'. Application of SSB with 'T. harzianum' increased germination by 20%, as well as a 70% increase in fresh and dry soybean mass in relation to the control. The agronomic indices evaluated in this study demonstrated that the use of SSB in conjunction with 'T. harzianum' presents a synergistic effect, allowing for better development of the soybean plants.