Resíduo mineral a partir de biomassas amazônicas como uma fonte alternativa de nutrientes para a agricultura

Abstract

The agrominerals and fertilizers deficiency in Brazil has acted as an obstacle to the country's consolidation plans as a world agricultural power and has placed damage on its trade balance. When we take the Amazon region as a reference, to which the expansion of the national agricultural border has been directed, this scenario has been even more unfavorable, since this region, in addition to having limited resources, also presents low developed technologies, which has increased the deforestation of large areas for low-yield agricultural production. In addition, in order to reduce dependence on fossil fuels, Brazil has been investing in modern biofuel production, mainly in the technological development of bioenergy conversion and production from lignocellulosic waste and energy forest plantations. Although the use of these bioenergy sources contributes to mitigating competition with food products and CO2 emissions problems, increase biomass uses, especially in the firewood and charcoal form, has caused an increase in the demand for fertilizers and has produced large quantities of mineral residues, which occur as biomass ashes. Therefore, one of the major challenges for the sustainable management of biomass residues as a source of renewable energy is the production of large quantities of ash, which are destined for disposal due to the lack of a recycling system. From an environmental and socio-economic aspect, ash recycling in agriculture and forestry soils can play an important role in facing the difficulty of integrating the use of renewable energy, fertilizers dearth, and organic and mineral residues management. Among the main advantages of the ash application in agricultural and forest soils are the ability to neutralize acidity and the ability to supply important nutrients to plants, such as Ca, Mg, P, and K. Although the agronomic effects of biomass ash are common knowledge, its application in the soil requires attention because textural and compositional variations can directly interfere in the solubility, availability, and absorption of nutrients. In addition, the response of the ash's fertilizing capacity depends on the properties of the soil, mainly pH, texture, and organic matter content. Thus, the applicability of biomass ash becomes more favorable after chemical, mineralogical, and agronomic tests. In this context, having as one of the biggest challenges of the Amazon region the residues management and the increased demand for fertilizer to attend the expansion of the agricultural border and the production of energy forests, the research aimed to evaluate the yield and composition of ash from Amazonian biomasses, as well as carrying out a first evaluation of the effects of these residues on the fertility of acid soils, with special attention to the P dynamics and the plant nutrition and yield. To this end, the mineral residue, generated by the açaí seeds and wood chips combustion and co-produced by a calcined phosphate fertilizer industry, was subjected to chemical and mineralogical analyzes, and to incubation tests with soils and plant. The results were used to estimate that the fertilizer industry produces ~ 4.7 – 9.9 tons/day of ash, which occurs as bottom ash and has a relatively low compositional variability throughout the year. Ash from Amazonian biomasses is mineralogically composed of amorphous phases, silicates, and oxides and chemically composed of SiO2, Al2O3, CaO, Fe2O3, P2O5, K2O, and MgO. The highest quantities of SiO2 and Al2O3 mainly result from quartz and kaolinite incorporated in the biomasses. By contrast, CaO and MgO originate from wood chips, whereas K2O and P2O5 originate from açaí seeds. According to the results of the soils incubations and the Avena sativa cultivation, the applications of ash from Amazonian biomasses promoted moderate effects in the correction of acidity in soils, produced increases in the availability of macronutrients (P, Ca, Mg, and K) and micronutrients (B, Cu, Fe, and Mo), and favored plant production and nutrition. In soils rich in organic matter content, the applications of biomass ash also positively affected the transformation of inorganic P into organic P. Even in high amounts, the biomass ash supply offered no risk salinity, nutrient immobilization, Al and Mn toxicity, and contamination by As, Cd, Cr, Hg, and Pb soil and plants. Therefore, the recycling of mineral residue co-produced by the combustion of Amazonian biomass in agricultural or forest soils may represent a sustainable and strategic alternative for the management of industrial waste and for the maintenance of the fertility of the dystrophic soils of the Amazon region. In addition, the application of biomass ash can be a great ally in reducing losses due to P precipitation in acidic soils in the region.