Dynamics of the superficial fluxes over a flooded rice paddy in southern Brazil

摘要

In Southern Brazil, rice paddies are an important agribusiness occurring in lowlands, where the growing season occurs in the summer and the area remains without use in the rest of the year. We estimated the surface fluxes (carbon dioxide (CO_2), Latent (LE) and Sensible (H) heat fluxes) over a flooded rice paddy in Southern Brazil for a five-year period using the eddy covariance methodology. LE was higher than H, with mean values of the Bowen ratio (H LE~(-1)) of 0.14 during the growing season and 0.35 during the fallow season. The mean evapo-transpiration (ET) was of 4.3 ± 0.3mm d~(-1) during the growing season and 1.8 ± 0.3mm d~(-1) during the fallow season. We related the gross primary production with the water use efficiency to obtain the partitioning of ET between evaporation (E) and transpiration (T). Annually, E and T represent approximately 50% of the ET. However, there is a marked seasonal variability in these components, mainly related to the variation of the leaf area index. Over the full five-year study period, the flooded rice paddy was a net carbon sink of 198 ± 221 gC m~(-2) y~(-1). The CO_2 flux presented high variability between the fallow and growing seasons. The fallow periods represent a source of 268 ± 123 gC m~(-2) y~(-1)and the growing seasons are a sink of 448 ± 105 gC m~(-2) y~(-1). During the annual period, the flooded rice paddy presents a low water use efficiency, 1.05 gC kgH_2O~(-1).