COMPRESSIBILITY OF A YELLOW LATOSOL UNDER DIFFERENT MANAGEMENT SYSTEMS WITH SUGARCANE

The application of sugarcane residues to the soil may induce changes in soil compressibility parameters. The objective of this study was to investigate the compressibility behavior of a dystrophic cohesive Yellow Latosol in the coastal tablelands of the state of Alagoas, in three different management systems with sugarcane, with different levels of organic residue application. The experiment was conducted in an area of sugarcane production (Usina Santa Clotilde), Alagoas. Three plots were chosen in sugarcane fields: sugarcane under irrigation (SMI), under fertigation with vinasse (SMV) and with application of vinasse + filter cake (SMVT). These management systems were compared to each other and to a control plot, represented by native forest (NF). The three sugar cane management systems had been established four years before soil sampling. Undisturbed soil were collected (layers 0-0.20 m and 0.20-0.40 m), using a metal sampler. The samples were first tested by uniaxial compression (gravimetric moisture levels of 0.10; 0.14; 0.18; and 0.22 kg kg(-1)). For the compression test, loads were applied with vertical tensions of 12.5; 25; 50; 100; 200; 400; 800 and 1600 kPa and readings taken every 30 sec. Thereafter, the samples were oven-dried for gravimetric moisture determination. The results were subjected to variance and multiple regression analysis of the pre-compaction tension, according to the following independent variables: bulk density (Ds), gravimetric moisture (Ug), mean weight diameter of water-stable aggregates (DMPu) and dissipated energy (Ed). The load carrying capacity of native forest soil was lower in both layers than in the three sugarcane managements; the management systems under sugar cane with organic residue application (SMV and SMVT) have lower tension levels; the limit curves (suction increase and loading collapse) can be used in the planning of mechanical operations and pre-compaction stress can be predicted from the physical properties.