RESUMO
Semiarid regions are characterised by water scarcity, a limiting factor on plant growth and development. The Sertão Canal was built in the semiarid region of Brazil, more specifically in the state of Alagoas, with the aim of making year-round irrigation possible. However, for the best water management, a physical and hydrological knowledge of the soils is necessary. As such, the aim of this study was to determine the physical and hydrological characteristics of three different types of soil (Argisol, Quartzarenic Neossol and Regolithic Neossol) under native vegetation (Caatinga) and agricultural systems in the semiarid region of Alagoas, as well as to adjust the soil water retention characteristic curves. Soil samples were collected at depths of 0-10, 10-20 and 20-30 cm in the municipalities of Inhapi, Delmiro Gouveia and Pariconha, in the state of Alagoas. The points of the moisture characteristic curve were determined by the Richards method, at pressures of 33, 100, 500, 1000 and 1500 kPa. Retention curves were modelled using the exponential decay equation and compared using the van Genuchten equation, modelled with the help of the RETC computer software. Particle size varied according to the textural classification of the different soils, from Sand to a Sandy Clay Loam. The retention curve fluctuated due to the particle size of the soil, with the Red-Yellow Argisol (Inhapi) having a greater capacity for water retention. Extremely sandy soils, such as those in the Delmiro Gouveia region, had a low capacity for retaining water. For each soil sample, the exponential decay equation gave the best fit, with values for R2adjust of greater than 0.93. When the measured soil moisture levels were compared with the levels estimated by the RETC model, some of the treatments were unable to estimate accurately the moisture levels obtained with the soil water retention curves.
Assuntos
Características do Solo , Bacias Hidrográficas , Umidade do SoloRESUMO
Studies show that soil organic carbon (SOC) decreases between 3 % and 9 % in degraded grasslands in tropical regions, mainly due to the absence of techniques to enhance carbon contribution to soils. This study assessed SOC stock change factors for grassland management, specific to the semi-arid region of Brazil. These factors may contribute to a better understanding of SOC dynamics and could be used to improve inventories on GHG emissions. In addition, they could be used for updating default factors used by the Intergovernmental Panel on Climate Change. This study considers both soil sampling and a literature review, and comprises 27 paired comparisons, where the dataset was analyzed using a mixed linear model. For the grassland in the Brazilian semi-arid region, the SOC stock is reduced by between 12 % and 27 % due to inadequate management, overgrazing, and edaphoclimatic conditions of the Brazilian semiarid. However, this depends on aspects, such as land use and soil layer, which represents substantially more severe losses than in other regions of the country. We also found that losses occur during the first five years after conversion of native vegetation. The results also indicated a trend for SOC stocks to recover over time, reaching 4 % after 30 years of use as grassland, probably related to the long period without soil tillage and the role of gramineas root system.(AU)
Assuntos
Carbono , Química do Solo/análise , Matéria Orgânica , Pastagens/análise , Zona Semiárida , BrasilRESUMO
Studies show that soil organic carbon (SOC) decreases between 3 % and 9 % in degraded grasslands in tropical regions, mainly due to the absence of techniques to enhance carbon contribution to soils. This study assessed SOC stock change factors for grassland management, specific to the semi-arid region of Brazil. These factors may contribute to a better understanding of SOC dynamics and could be used to improve inventories on GHG emissions. In addition, they could be used for updating default factors used by the Intergovernmental Panel on Climate Change. This study considers both soil sampling and a literature review, and comprises 27 paired comparisons, where the dataset was analyzed using a mixed linear model. For the grassland in the Brazilian semi-arid region, the SOC stock is reduced by between 12 % and 27 % due to inadequate management, overgrazing, and edaphoclimatic conditions of the Brazilian semiarid. However, this depends on aspects, such as land use and soil layer, which represents substantially more severe losses than in other regions of the country. We also found that losses occur during the first five years after conversion of native vegetation. The results also indicated a trend for SOC stocks to recover over time, reaching 4 % after 30 years of use as grassland, probably related to the long period without soil tillage and the role of gramineas root system.