Production, soil amendment and sustainability of sugarcane trash biochar

Abstract

In the past, sugarcane was harvested manually with the aid of fire to facilitate cutting. And because of the Law of the State of São Paulo n. 11,241, which establishes the end of the use of the burning, the sugarcane trash that was previously burned, today is a residue in the plantations. To add value and give a better destination to this residue, some alternatives for its use as raw material are studied. Biochar is a product of pyrolysis of biomass, rich in carbon, which has qualities as a soil conditioner. Therefore, the objectives of this thesis were: to verify the best conditions (pyrolysis temperature and residence time) for biochar production of sugarcane straw and its characterization (Chapter 2), how the biodegradation of this biochar influences for carbon sequestration (Chapter 3) and check the development of sugarcane seedlings with the addition of percentages of biochar in soil (Chapter 4). To verify the best conditions for biochar production (Chapter 2), 6 treatments with 3 different pyrolysis temperatures and 2 residence times were chosen: 200 °C - 2 hours, 200 °C - 4 hours, 325 °C - 2 hours, 325 °C - 4 hours, 450 °C - 2 hours, 450 ° C - 4 hours. The treatments were submitted to proximate analysis, gravimetric yield, porosity, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy analysis (FTIR), X-ray diffraction analysis (XRD) and hydrophobicity test. For biochar biodegradation (Chapter 3), the treatments were: sugarcane straw in natura, 200 °C - 2 hours, 325 °C - 2 hours, 450 °C - 2 hours. These biochars were characterized by their elemental composition (C - carbon, H - hydrogen, N - nitrogen). The biochar (6.3 g/flask) was incubated in 4 flasks by treatment with characterized soil. The quantification of the gases (CH4, CO2, NO2) was performed to verify the influence of biochar on carbon sequestration will occur in a period of 85 days, one sampling per week. For pot experiment (Chapter 4), the biochar produced at 330 °C - 1 hour was mixed to the soil in different application rates: 0 t ha- 1, 1 t ha-1, 5 t ha-1, 15 t ha-1, 30 t ha-1. It was installed 15 plots per dosage/treatment, totalizing 150 plants. Height and diameter measurements were collected every 20 days for 257 days. At the end of the pot experiment it was obtained the dry mass of the aerial part and roots. The soil used was analyzed chemically before and after the pot experiment. The results of the characterization of the biochar produced by Chapter 2, showed that the pyrolysis temperature was a factor that has more influence on the final characteristics of the biochar than the residence time. In Chapter 3, it was observed that the highest rates of greenhouse gas (GHG) emissions were released by treatments with in natura and with biochar 200 ° C, with treatments at 325 °C and 450 °C being more stable and resistant to biodegradation. In Chapter 4, the incorporation of biochar did not result in improvements in the growth of sugarcane but did influence the increase in the pH of the soil. In general, the 325 °C biochar with 2 hours of residence time showed enough results for its application to the soil. Biochar has also proved to be a viable alternative for reducing GHG emissions.