Mechanical Behavior of an Ultisol Under Different Sugarcane Management Systems in Brazil

Compressibility and shear strength in agricultural soils are associated with pressures exerted on the soil surface by the intensive use of machines. This study aimed to evaluate the mechanical behavior of an Ultisol cultivated with sugarcane under the application of sugarcane residues (vinasse and filter cake) and compare it with an Atlantic Forest soil. Uniaxial compression tests were performed through the application of increasing with pressures from 12.50 to 1,600 kPa, at three water contents in undisturbed samples from the layers of 0-0.20 and 0.20-0.40 m, and for shear direct test were collected in the layers of 0-0.20 m and, subjected to three water content levels and four levels of normal tensions of direct shear. The higher content of total organic carbon in the soil under native forest (2.42 g kg-1) allowed higher pre-compression stresses (101.21-143.55 kPa) due to an increase in soil cohesion from 22.58 to 61.23 kPa, with the reduction in the volumetric water content. Thus, this natural condition was significantly different from the management systems, with respect to the mean values of cohesion, by Tukey test (p<0.05). The application of filter cake and vinasse for 25 years significantly favored the dissipation of pre-compression stress in the soil, compared with the soil under native forest. The system with filter cake application showed higher shear strength from the tension of 100 kPa on, with values from 120 to 190 kPa, in comparison to the system with vinasse application.