The main objective of this paper was to verify the suitability of the S index, defined as the slope of the soil water retention curve at its inflection point, in the diagnosis of the physical quality of Brazilian 'Cerrado' soils. A total of 2364 samples were selected from the soil data set of Embrapa Rice & Beans and Embrapa Cerrados, covering 'Cerrado' soils from Mid-West, North, and Northeast regions of Brazil. Values of S index obtained from these samples were correlated to bulk density of soil, macroporosity, and total porosity, considering the following textural classes: highly clay, clay, sandy clay, sandy clay loam, loam/sandy loam and loamy sand/sand. Based on review of literature, critical values were established for the physical attributes that separated, according to the texture, soils with good and poor structural quality and, based upon these, critical values for the S index were established. This index was highly correlated to the physical attributes, showing itself to be an adequate indicator of physical quality of 'Cerrado' soils. The limit value of S = 0.045 showed to be adequate to separate soils with good structure and soils with the tendency to be degraded, while values of S≤0.025 indicate physically degraded soils.
soil texture; bulk density; soil porosity
