Abstract
As part of efforts to reduce pressure on the Amazon and other biomes, one approach considered by Brazilian authorities and scientists is more intensive use of the soils of the interior of the northeast of the country, which are generally sandy, with low contents of organic matter and low water holding capacity and are frequently affected by severe droughts. In this work, biochars produced from waste biomasses were tested for the improvement of these soils. The highest BET (Brunauer-Emmett-Teller) specific surface areas were observed for all biochars. In the pH range studied, the water hyacinth plants (WH) sample showed the most negative zeta potentials, as well as the highest water holding capacity (WHC) values, while the zeta potentials of two quartzarenic neosol soils were consistent with their WHC values. The results suggested that despite the effect of porosity on water retention, the zeta potential could be associated with the presence of negative charges by which hydrated cationic counterions were absorbed and retained. The surface energy and its polar and dispersive components were associated with water retention, with sugar cane bagasse, orange peel, and water hyacinth biochars presenting higher SE values and larger polar components.
Highlights
In a book chapter published by the American Chemical Society[1], it was observed that the addition of biochar, obtained cheaply from agricultural waste biomasses and produced on the farms themselves, increased the water holding capacity (WHC) of these soils
The slow pyrolysis, which was a focus of this study, caused the release of volatile organic matter, hemicellulose, and lignin, together with shrinkage, melting, and cracking, which improved the porosity of the materials[19,20]
Other secondary parameters influenced the WHCs of the biochars, including the zeta potential and the cation exchange capacity
Summary
In a book chapter published by the American Chemical Society[1], it was observed that the addition of biochar, obtained cheaply from agricultural waste biomasses and produced on the farms themselves, increased the WHCs of these soils. The use of pyrolyzed biomass residues in soils arose from research studies of the Amazonian soil known as “Terra Preta de Índios” (TPI) These soils, which were used by a number of tribes and covered large areas, were enriched with biomass charred by farmers. Biochar is produced by the thermal decomposition of biomass in an oxygen-deficient atmosphere over a wide range of temperatures, from 300 to 1000 °C5, in a process known as pyrolysis It is a fine-grained carbonaceous material with high organic carbon content and is largely resistant to chemical and biological decomposition (mineralization)[6]. The direct effect is related to its large internal surface area and the high amount of residual pores, where water is retained by capillarity This improves overall soil porosity and increases the soil water content, decreasing the mobility of the water and reducing water stress in plants. An indirect effect is improvement of soil aggregation and structure, affecting the water retention capacity of the soil[17,18]
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