The GPR uses indirect technique for investigation of subsurface structures, characterized as non-invasive method, which allows to extract information throughout the soil profile without drilling, probing or digging. This study aimed to evaluate the use of GPR in the establishment of soil physical properties in a area under sugar cane, and its correlation with the volumetric cylinder method. The study area in Bom Sucesso, State of Paraná (Brazil), had been used for sugar cane cultivation for over 20 years. Undisturbed soil samples were obtained by the core method from the layers 0-0.1, 0.1-0.2, 0.2-0.3, 0.3-0.4 and 0.4-0,5 m, along three parallel transects, the central corresponding to the row of plantation (transect 2) and the outer two to the inter-rows (transects 1 and 3). Density and porosity were determined first based on physical samples to check the soil status in sugar cane rows and inter-row in the five layers. These values were subsequently correlated with the dielectric constant values (K) obtained by the GPR, although for the 0.4-0.5 m layer only; the surface layers to a depth of 0.4 m could not be assessed due to technical limitations of the equipment and physical and chemical soil properties, which ultimately invalidated the observations. The density in the inter-row was higher than in the planting row, with statistical differences between the layers 0-0.1 and 0.2- 0.3 m. Total porosity was lower in the inter-rows, differing significantly from the rows in the 0-0.1 m layer. The K values were higher in the rows, where moisture and porosity were higher, and lower in the inter-rows, where the densities were close to the critical limit. The correlation of K with density and porosity was not significant. Small changes in soil porosity with increasing density were sufficient to decrease the K value in the inter-rows, due to the reduction in the water content in the pores. This fact was confirmed by the correlation of K with moisture. It can therefore be concluded that the GPR was extremely sensitive to soil moisture variations, with better results for this variable than for density and porosity determined by the volumetric cylinder.
physical properties; dielectric constant; reflection
