EFLUXO DE C-CO2 E ATRIBUTOS FÍSICOS DO SOLO DE DUAS ENCOSTAS SOB PASTAGEM

Abstract

The carbon quantity stored in the organic matter of the soils is twice higher compared to the carbon found in the atmosphere, in the form of CO2. Pastures contribute in a large part of these quantities of carbon stored in the soil, therefore, emissions in pasture need to be better quantified in order to know the behavior of the CO2 emissions throughout the year. Based on that, the aim of this study was to physically characterize e evaluate the C-CO2 efflux of the soil, along a slope in different positions (shoulder, half-slope and pediment) in two slopes during the rainy season. The experiment was carried out in the microbasin of Vaca Brava, located between the municipalities of Areia and Remígio - Paraíba. The slopes where the present study was performed are composed by the position of the shoulder, half-slope and pediment, where were collected the soil samples for physical analysis, at each position and in the same positions was evaluated the efflux of C-CO2 over time. On every evaluation date, the precipitation on both slopes was recorded. To analyze the data, a 2x3x5 factorial scheme was used, which correspond to the two slopes, one slope under 20 years of pasture and one slope under 1 year of pasture, three relief positions (shoulder, half slope and pediment) and 5 rainfall quantities throughout the year. The CO2 efflux was weekly evaluated until the end of the rainy season, by the amount of CO2 captured on the soil surface, and capture of carbon dioxide (CO2) inside static chambers, by 40 mL of a solution of sodium hydroxide (NaOH) to 1 Mol L-1 contained in a vessel for 24 hours. The mean of C-CO2 efflux values of the soil were submitted to analysis of variance and when relevant compared to the means of the positions by the Tukey test (P≤0.05). In the shoulder position, the highest values were verified in the first collections, in May, June and July of 2016, in the wettest months, while in the drier months the lowest values of C-CO2 emissions were observed. In the half-slope and pediment positions, there was a tendency to increase soil C-CO2 emissions, in the highest rainfall, similar behavior in both pastures, due to the intimate relationship between soil moisture and microbial activity, and in periods when the soil water content is low, there is a reduction in microbial activity and consequently a decrease of C-CO2 emissions. In the slope under 20 years of pasture, the highest emissions were obtained at the pediment position in all of precipitations higher than 1.6 mm. It was concluded that between the positions of the slopes, the one with the highest C-CO2 emission values was the pediment, in the two slopes under pasture, and that the soil carbon emissions are directly proportional to rainfall.