Quantifying critical pressures for plant growthCompaction is one of the main causes of degradation of agricultural soils and it has been evaluated through several indicators of: (a) soil structural quality for crop growth, such as the least limiting water range (LLWR), and (b) load support capacity of the soil, i.e., the preconsolidation pressure (σp). This research was carried out with the objective to relate the LLWR and the σp, as well as to determine critical pressures values that can be applied to the soil without inducing restrictive conditions to plant growth as well as additional soil compaction. The study was conducted with soil samples of a Red-Yellow Podzolic soil (Ultisol) cultivated with sugarcane from Piracicaba, State of São Paulo (Brazil). Thirty six undisturbed soil samples were taken at the superficial layer to quantify the σp and the LLWR. Soil critical bulk density (Dbc) was obtained from the LLWR. The σp was a linear function of the water content and soil bulk density, allowing the incorporation of Dbc and LLWR for quantifying the Pcr. The results indicated that Pcr decreased linearly with soil water content, varying from 360 kPa to 500 kPa for the soil water range from θ = 0,18 m³ m-3 to θ = 0,12 m³ m-3. The results allowed to define values of maximum pressures that can be applied to the soil, for different water contents, without promoting degradation of soil structural quality for plant growth.
soil compaction; preconsolidation pressure; least limiting water range; critical pressure values