Biochar from eucalyptus waste improves the chemical and biological properties of an Inceptisol and sugarcane yield over time under tropical conditions

In recent years, many studies have demonstrated the positive effects of biochar on soil; however, its use in large agricultural areas is still considered controversial, as the quantities used in studies with potted plants are very high when extrapolated to crops in the field. The aim of this study was to evaluate the effects of biochar on soil properties and sugarcane productivity over five years. The experiment was carried out in a randomized block design with a 5 × 2 factorial design and four replicates. These factors corresponded to the biochar doses (no biochar, 10, 20, 30, and 40 Mg ha^-1) with and without the NPK mineral fertilizer. The biochar was produced from eucalyptus wood by slow pyrolysis at 350 °C, and uniformly incorporated into the planting furrow in the 0 to 20 cm layer. Every year for five years, soil and plant samples were collected for laboratory analysis, and sugarcane yield was assessed. Maximum sugarcane stalk productivity, 154 and 146 Mg ha^-1, was obtained with the application of 37.71 and 31.00 Mg ha^-1 of biochar in treatments with and without NPK fertilizer, respectively. Biochar doses increased nutrient availability, cation exchange capacity, soil organic carbon, the number of arbuscular mycorrhizal fungal spores, and glomalin. There was no effect of the treatments on total N and diazotrophic bacteria (Azospirilum spp., Herbaspirillum spp., and Gluconacetobacter spp.).