Fluxos de CO2 e de vapor d’água em feijão cultivado no agreste meridional pernambucano

Abstract

Many important processes occurring in ecosystems, such as photosynthesis and productivity of vegetation, are associated with the exchange of CO2, water and energy. Accurate measurement of these fluxes are therefore fundamental to a broad understanding of the carbon cycle in terrestrial ecosystems. However, no such study was conducted under the conditions of the Agreste of Pernambuco, with the bean crop. Given the above, this study aimed to quantify the water, energy and CO2 fluxes in soil cultivated with bean under rainfed conditions. The study was conducted in a bean producing area of the city of São João, where were installed sensors to measure these fluxes, using the energy balance method - eddy covariance (energy and CO2 fluxes) and soil water balance method (water fluxes) in the period from 31/05/2013 to 08/20/2013. In addition to these measurements were also measured height, leaf area index (LAI) and the bean yield. Regarding the components of the water balance was found that the flow of water at a depth of 35 cm (deep drainage and/or capillarity rise) had very low values. It was also observed that the periods of high rainfall resulted in higher water storage in soil and increased evapotranspiration (ET). The ET obtained by water balance method had a total and average values of 146.0 mm and 1.78 mm d-1, respectively. The bean presented its highest water consumption during the reproductive period (29/06/2013 to 29/07/2013), with an average value of 2.55 mm d-1. Regarding the energy fluxes, it was found that the latent heat flux (LE) consumed on average 78.46% of the radiation (Rn). The ET, measured by the eddy covariance method, was total value of 179.3 mm, with a mean value of 2.2 mm d-1. Bean yield was 2,050 kg ha-1, with water use efficiency of 1.16 kg m-3. Regarding the CO2 fluxes, it was observed that the same varied from -11.21 to -0.75 mol m-2 s-1, indicating the occurrence of carbon sequestration by the crop. On average, bean sequestered 54 kg C ha-1 per day, the equivalent to 3.3 t C ha-1 during the trial period.