Soil physical changes induced by sugarcane cultivation in the Atlantic Forest biome, northeastern Brazil

Abstract

In northeastern Brazil, the sugarcane expansion has occurred historically over the Atlantic Forest biome. However, little is known about the physical process and changes induced by sugarcane cultivation in this biome. Thus, a field study was conducted to evaluate changes induced by sugarcane cultivation on soil physical properties, processes and functions in the Atlantic Forest biome. For that, soil samples were collected at three sites in northeastern Brazil: AF – Atlantic Forest, SCratoon – successive sugarcane ratoon cultivation and SCtill – tilled soil for sugarcane replanting. Quantitative and semi-quantitative soil properties [i.e. bulk density, soil penetration resistance (SPR), water-stable aggregates, soil organic carbon (C), pore size distribution and Visual Evaluation of Soil Structure (VESS) scores] were examined. In addition, four critical soil functions were evaluated by a soil physical quality index (SPQI). Atlantic Forest soil presented the greatest soil physical quality (i.e. lower bulk density, higher porosity, soil C and soil aggregate stability), functioning, according to SPQI, at 88% of its full capacity. However, SPR under AF was significantly higher than SCratoon and SCtill. Soil tillage reduced SPR in SCtill compared to the area under successive sugarcane cultivation (SCratoon). The results revealed that the high SPR in AF and SCratoon areas occurred without soil volume variation (i.e. no compaction) in relation to the SCtill, indicating that these soils are susceptible to hardening induced by C bonds and thixotropy processes. Soil tillage for sugarcane replanting resulted in immediate improvements on physical conditions for root growth by decreasing SPR; however, soil disturbance increases its susceptibility to degradation by reducing water-stable soil aggregate, organic C and aeration pores. Thus, sugarcane cultivation declined the performance of soil physical functions to 72 and 67% of its full capacity in SCtill and SCratoon, respectively. Finally, best management practices to reduce soil disturbance and increase C should be prioritised, as well as minimising the mechanisms responsible by soil hardening in order to reduce soil physical degradation and improve the environment for root growth in sugarcane fields.