Land use change, soil physical properties and carbon stocks at a sandy soil domain of a Cerrado agriculture frontier

• Autor(a) principal: Silva, Emily Ane Dionizio da
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: https://locus.ufv.br//handle/123456789/27676
• topic: Meteorologia Aplicada; Física do solo; Carbono; Solos arenosos; Agricultura; Cerrados

The rapid expansion of agriculture in the Brazilian Cerrado has raised concerns about water resources conservation and about greenhouse gases emissions. The largest and most dynamic agricultural frontier of the country known as MATOPIBA is located in this biome, also the largest producer of cotton, the Western Bahia. In order to evaluate how the land use changes affect the physical and hydraulic soil properties and carbon emissions in this region, this study collected data on physical soil properties and carbon stocks for different land use, land cover types, and developed an historical reconstruction of spatial patterns of carbon stocks during the 1990-2018 period. There are seven main conclusions in this thesis: First, intensive soil use increases soil compaction and reduces the saturated hydraulic conductivity (water infiltration velocity) of the soil. Analysis of physical and hydraulic properties indicate that soils under intensive use (Irrigated Agriculture, Rainfed Agriculture and Pasture) present higher density and lower saturated hydraulic conductivity than soils under natural vegetation (Forest Formations and native Cerrado). Second, intensive land use can increase the occurrence of surface runoff events. Although soils of Western Bahia present high infiltration capacity, its intensive use decreases this capacity and increases the chances of erosion. For rainfall with intensity of 50 mm hour-1, surface runoff is expected in 62% of Irrigated areas, 41% of Pasture areas, 29% of Rainfed Agriculture areas, 15% of Forest areas and 5% of the Cerrado areas visited. For rainfall with intensity of 100 mm hour-1, it is expected that surface runoff will occur in 95% of Irrigated areas, 73% of Pasture areas, 62% of Rainfed Agriculture areas, 20% of Forest areas and 32% of Cerrado areas visited. Absence of runoff should occur only in cases of rainfall intensity of less than 10 mm hour -1 or less. Third, it is extremely likely that the replacement of Forest Formations by Pasture implies in a reduction of SCS100 by 37.3% (p-value = 0.031), and it is very likely that the replacement of Forest Formations by Rainfed Agriculture reduces SCS100 by 30.3% (p-value = 0.053). Fourth, it is likely that conversion of savanna formations to Rainfed Agriculture or Pasture decreases SCS100 by 18.2%(p-value = 0.269) and 26.4% (p-value = 0155). Fifth, it is more likely than not that the conversion of Forest Formations to Irrigated Agriculture reduces SCS100, and that conversion of Cerrado Formations to Irrigated Agriculture increases the SCS 100 by 11.1% (p-value = 0.455). Sixth, it is extremely likely that the conversion of Pasture (p-value = 0.022) or Rainfed Agriculture (p-value = 0.034) to Irrigated Agriculture increases SCS100 . Finally, it was estimated that, historically, Western Bahia lost 7.74% of the total carbon stock, with a decrease from 112 Tg-C in 1990 to 103 Tg-C in 2018. Despite the limitations and uncertainties associated with our results, it is possible to conclude that the impacts of land use change are a reality on the agricultural frontier of the Cerrado and there is an urgent need to monitor how these changes occur over time. A temporal monitoring of these effects is crucial to identify management practices and the time scale needed to change the carbon loss trend, contributing to the development of effective gas emission mitigation strategies and the development of sustainable agriculture in the region.