Remote Sensing for Mapping Soybean Crop in the Brazilian Cerrado

The soybean expansion in the Brazilian Cerrado has been strongly affected by internal and external markets. The main factors driving that expansion are the climatic conditions, the development of technologies and genetic improvement. Recent studies have shown that the soybean expansion has become a major cause of reduction of native vegetation in Mato Grosso State - Brazil, responding for 17% of deforestation from 2000 to 2004. This work aims to map soybean areas in the Brazilian Cerrado in Mato Grosso State, using MODIS data. Thirteen MODIS images (MOD13 - 16 days composition), acquired from September, 2005 to March, 2006, were used to run principal component analysis (PCA) in order to reduce the dimensionality of the data. The first three components (PC1, PC2 and PC3), which contained about 90% of data variability were segmented and utilized as input for an unsupervised classification using the ISOSEG classifier, implemented in the SPRING software. Eighty field work points were randomly selected for the accuracy assessment. An intersection between the soybean map and a map generated by the "Project Monitoring Deforestation of Brazilian Biomes Satellite - PMDBBS", which aimed at identifying anthropic areas, was conducted in order to evaluate the distribution of soybeans within those areas. Moreover a soil map was used in order to evaluate the soybean distribution over the classes of soil. The classification result presented overall index of 83% and the kappa coefficient of 0.64 for the soybean map, which presented a total soybean area of about 42,317 square kilometers. Furthermore, it was verified that 27% of anthropic area was covered by soybean. In relation to the soil analysis, 87% of the total soybean area was planted in Oxisoils. Despite the economic gain related to the soybean production, an adequate management is needed to avoid soil acidification, soil erosion and pollution, aiming at providing a sustainable environment.