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This study is based on the importance of biological control methods and the lack of information on the effect of biochar (BCH) from sewage sludge associated or not with Trichoderma harzianum on the control of Macrophomina phaseolina in the bean crop (Phaseolus vulgaris, cv. BRS Estilo). Biochar from sewage sludge, pyrolyzed at 500 ºC and used in low concentration (0.5%), has a direct effect on the in vitro control of M. phaseolina. However, higher BCH concentrations stimulated the growth of the pathogen. In culture medium with or without BCH, T. harzianum (strain 1306) inhibited the mycelial growth of M. phaseolina. The addition of BCH + T. harzianum reduced the deleterious effects caused by M. phaseolina on bean plants. This study demonstrated that joint application of BCH from sewage sludge + T. harzianum considerably increased the fresh and dry mass of bean plants, inoculated or not with M. phaseolina.

The thermochemical transformation of sewage sludge (SS) to biochar (SSB) allows exploring the advantages of SS and reduces possible environmental risks associated with its use. Recent studies have shown that SSB is nutrient-rich and may replace mineral fertilizers. However, there are still some questions to be answered about the residual effect of SSB on soil nutrient availability. In addition, most of the previous studies were conducted in pots or soil incubations. Therefore, the residual effect of SSB on soil properties in field conditions remains unclear. This study shows the results of nutrient availability and uptake as well as maize yield the third cropping of a three-year consecutive corn cropping system. The following treatments were compared: (1) control: without mineral fertilizer and biochar; (2) NPK: with mineral fertilizer; (3) SSB300: with biochar produced at 300 °C; (4) SSB300+NPK; (5) SSB500: with biochar produced at 500 °C; and (6) SSB500+NPK. The results show that SSB has one-year residual effects on soil nutrient availability and nutrient uptake by maize, especially phosphorus. Available soil P contents in plots that received SSB were around five times higher than the control and the NPK treatments. Pyrolysis temperature influenced the SSB residual effect on corn yield. One year after suspending the SSB application, SSB300 increased corn yield at the same level as the application of NPK. SSB300 stood out and promoted higher grain yield in the residual period (8524 kg ha−1) than SSB500 (6886 kg ha−1). Regardless of pyrolysis temperature, biochar boosted the mineral fertilizer effect resulting in higher grain yield than the exclusive application of NPK. Additional long-term studies should be focused on SSB as a slow-release phosphate fertilizer.

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 °C 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.