Sugarcane harvesting systems in northeastern Brazil: Effects on the physical, chemical and biological attributes of the soil

Sugarcane is one of the main agricultural crops in Brazil, with significant socioeconomic importance. However, different harvesting systems, such as burning and unburnt cultivation, promote changes in soil attributes. This study aimed to evaluate the influence of adopting an unburnt mechanized sugarcane harvesting system, transitioning from a system with burning and native vegetation, on the physical, chemical, and biological attributes of the soil in northeastern Brazil. The research was conducted in two sugarcane mills in the state of Alagoas, where four treatments were evaluated in each area: two mechanized harvesting systems, one system with harvesting preceded by burning, and an area of native vegetation, totaling 12 sampling points. The data were analyzed through multivariate analyses, including principal component analysis, hierarchical clustering, and the relative importance of variables. The results show that the conversion of native vegetation into sugarcane cultivation areas promoted the loss of soil organic carbon, which ranged between 7% and 62%, and reduced soil quality due to losses of particulate organic matter, microbial carbon, and increased density, corroborated by changes in other indicators, such as an increase in the metabolic quotient and degree of soil compaction. Despite the losses when compared to native vegetation, the unburnt system showed an increase in soil organic carbon, particulate organic matter carbon, a reduction in density, and an increase in microbial carbon, corroborated by changes in other indicators, such as a reduction in the metabolic quotient and soil compaction and an increase in the soil structural stability index.