ALTERAÇÃO DE USO DA TERRA NA REGIÃO MATOPIBA E A RELAÇÃO DA AGRICULTURA IRRIGADA E ESTOQUE DE CARBONO ORGÂNICO DO SOLO NO MUNICÍPIO DE SÃO DESIDÉRIO-BA

Abstract

The MATOPIBA region, encompassing parts of the Brazilian States (Maranhão, Tocantins, Piauí, and Bahia) has become one of the country’s main agricultural frontiers. This process has led to intense landscape transformation, marked by the rapid conversion of native vegetation into mechanized agricultural areas. The objective of this study was to analyze the spatiotemporal dynamics of land occupation and use in the MATOPIBA region from 1985 to 2023 with a particular focus on the municipality of São Desidério, Bahia (BA), a major hub of irrigated agriculture. Additionally, the study investigated the expansion of center pivot irrigation and its relationship with Soil Organic Carbon (SOC) stocks and the Normalized Difference Vegetation Index (NDVI). The methodological approach combined remote sensing products and Landsat time series processed through the MapBiomas plataform, and multitemporal statistical analyses, including the Mann-Kendall trend test and Sen’s Slope estimator. Data from the MapBiomas Solo database were also used to assess changes in organic carbon stocks across different classes (0–10; 10–20; 20–30; 30–40; 40–50; 50–60; 60–70; 70–80, and >80 t ha⁻¹). The data indicated a pronounced reduction in native vegetation cover and in land-use mosaics across the MATOPIBA region, with a statistically significant trend of loss (τ<0; p<0.001). In contrast, mechanized agriculture expanded rapidly, particulary soybean cultivation (+8,737 ha/year⁻¹) and cotton (+1,479 ha/year⁻¹). A strengthening core of irrigated agricultural production was identified in the São Desidério municipality, supported by the rapid expansion of center pivot irrigation systems (τ=0.989; Sen’s slope=+1,200 ha/year⁻¹). Conversely, water-related land cover classes showed an average reduction of -29 ha/year⁻¹, indicating increasing pressure on the Urucuia aquifer. Regarding to organic carbon, a redistribution of SOC stocks was found as characterized by annual decreases of -882 ha in the >80 t ha⁻¹ class and -138 ha in the 70-80 t ha⁻¹ class, accompanied by an expansion of intermediate classes, especially the 60-70 t ha⁻¹ category (+510 ha/year⁻¹). Comparisons between irrigated and non-irrigated areas indicated that mean SOC stocks (t ha-1) remained consistently higher in irrigated areas, with a stable relative difference raging from 47% to 66%. NDVI results showed low values in areas where native vegetation was removed during the initial phase of agricultural expansion. However, NDVI values increased after 2010, especially in irrigated agricultural areas. These findings suggested that center pivot irrigation contributes to greater stability of soil carbon stocks in sandy soils. Nevertheless, irrigation alone is insufficient to sustain high SOC levels without the implementation of conservation practices, such as no-tillage systems, crop rotation, and permanent soil cover. Overall, the results highlights the MATOPIBA region, particularly São Desidério, as a crucial centers of Brazilian agriculture, where high agricultural productivity is closely linked to significant social and environmental challenges. Irrigation emerges as a crucial factor in maintaining intermediate carbon stocks and enhance production resilience. However, its maximum effectiveness depends on integration with sustainable land management practices and public policies that reconcile food security, environmental conservation, and climate change mitigation. Furthermore, the results highlight the importance of combining mean indicators, class-based distributions, and annual maps for regional and municipal-scale monitoring, supporting both scientific debate and the development of public policies related to irrigated agriculture and carbon markets in Brazil.