Geotecnologia na caracterização da expansão do cultivo da soja no sul do Rio Grande do Sul

Abstract

Soybean cultivation is the main agricultural activity in Brazil. Its economic importance stems from the versatility of the grain in the industry that can be used for human consumption, for animal husbandry and for the production of biofuels. The quantification of agricultural areas with soybeans in Brazilian municipalities is carried out using an IBGE methodology called Pesquisa Agrícola Municipal-PAM, which is based on a subjective survey, which does not imply measuring the area. Therefore, the importance of using other more accurate methodologies to map soybean areas is justified, which are carried out objectively and produce results that can be used later as important information in the planning of public policies aimed at soybean cultivation. One of these methodologies consists of the use of images generated by means of sensors on board satellites, which makes it possible to map the expansion of soybean areas over other land uses/covers, and thereby assess the impact of this expansion on the region's economy. The present study aimed to map the areas cultivated with soybeans in the municipalities of Jaguarão, Arroio Grande and Santa Vitória do Palmar between 1999 and 2022. The mapping of soybeans during this period made it possible to verify which uses/coverages soybeans expanded and to evaluate the impact on the economic aspect of the municipalities. Images from Landsat 5, 7 and 8 platforms were used in the Red, Near Infrared and Medium Infrared bands from December to May of each crop year. Mapping was performed through supervised classification with the Random Forest machine learning algorithm in the geographic Information System Qgis. For the three municipalities studied, the supervised classification generated kappa index values considered excellent, there was an expansion of areas cultivated with soybeans, the classes that most gave way to soybeans were pasture and rice, and an increase in the participation of the crop in the municipal GDP was observed during the period studied. Comparing the profitability of soybean cultivation with rice cultivation, the latter proved to be more profitable. The occupation of soy in the mapped areas seems to be more profitable for the rural producer than traditional occupations such as native pasture, but it is not more profitable than the alternative occupation of rice. It can also be suggested that the increase in soybean area contributed to the increase in the GDP of the municipalities studied.