Ideal subsoiling moisture content of Latosols used in forest plantations

The interaction between moisture and soil significantly affects the performance of soil tillage equipment. This interaction has not been sufficiently studied for the subsoiling of forest areas in Brazil. For this reason, this study was conducted with the objectives of evaluating the degree of soil disturbance as a function of increasing clay and moisture contents, the relationship between soil resistance to penetration plus bulk density and moisture content, and establishing an ideal soil moisture interval for subsoiling, as a function of soil disturbance and bulk density. The research plots were established in a sandy clay loamy dystrophic Red Latosol (LVd-1), a kaolinite-rich clayey dystrophic Red Latosol (LVd-2), and a clayey dystrophic Red Latosol (LVd-3). The higher clay and organic matter contents in the LVd-3 imparted lower soil resistance to penetration, in view of the greater water adsorption of this soil. The three Latosols presented an inverse and quadratic relation between soil disturbance and moisture content increase. The increase in clay and kaolinite contents in these soils caused lower soil maximum densities and higher amounts of water required to reach their maximum densities. The LVd-1 showed better subsoiling conditions between the moisture contents of 0.07 and 0.13 cm3 cm−3, the LVd-3 between moisture contents of 0.14 and 0.27 cm3 cm−3, while the kaolinitic LVd-2 presented the lowest water range for subsoiling when compared to the other soils, between the moisture contents of 0.12 and 0.19 cm3 cm−3. The subsoiling water interval was based on two parameters (standard Proctor test and soil disturbance area) that may present much variation. These limitations suggest that new studies should be conducted to determine whether this interval should be adopted as an index for consideration when deciding upon the best condition for soil tillage.