ORBITAL AND LABORATORY SPECTRAL DATA TO OPTIMIZE SOIL ANALYSIS

Traditional soil analyses are time-consuming with high cost and environmental risks, thus the use of new technologies such as remote sensing have to be estimulated. The purpose of this work was to quantify soil attributes by laboratory and orbital sensors as a non-destructive and a nonpollutant method. The study area was in the region of Barra Bonita, state of Sao Paulo, Brazil, in a 473 ha bare soil area. A sampling grid was established (100 x 100 m), with a total of 474 locations and a total of 948 soil samples. Each location was georeferenced and soil samples were collected for analysis. Reflectance data for each soil sample was measured with a laboratory sensor (450 to 2,500 nm). For the same locations, reflectance data was obtained from a TM-Landsat-5 image. Multiple linear regression equations were developed for 50% of the samples. Two models were developed: one for spectroradiometric laboratory data and the second for TM-Landsat-5 orbital data. The remaining 50% of the samples were used to validate the models. The test compared the attribute content quantified by the spectral models and that determined in the laboratory (conventional methods). The highest coefficients of determination for the laboratory data were for clay content (R-2 = 0.86) and sand (R-2 = 0.82) and for the orbital data (R-2 = 0.61 and 0.63, respectively). By using the present methodology, it was possible to estimate CEC (R-2 = 0.64) by the laboratory sensor. Laboratory and orbital sensors can optimize time, costs and environment pollutants when associated with traditional soil analysis.