Analysis of CO2 Fluxes over soybean crops under two different tillage systems

Understanding the physical (and biological) interactions between the surface and the atmosphere, specially carbon dioxide (CO2) fluxes has a great scientific relevance. The aim of this study is to compare CO2 fluxes from soybean cropsmanaged under two different systems: conventional tillage and no-tillage. The conventional tillage operates in harrow or disk plow followed by a slight grade, while no-tillage is the establishment of cultures directly through crop residues retained on the surface of the soil. The measurements were performed with two micrometeorological towers, installed in the center of the soybean plots (measuring 60 x 40 cm) during the southern hemisphere summer (2009/2010). Data were collected in the experimental site located at Cruz Alta region, in southern Brazil. This site is part of the Rede Sul-brasileira de Fluxos Superficiais e Mudanças Climáticas (SULFLUX -http://www.ufsm.br/sulflux). The sensor used to measure wind components was a Campbell three-dimensional sonic anemometer (CSAT 3) and CO2 concentrations were obtained with an open path infrared gas analyzer LI-COR (LI-7500). The sensors were installed at a 2.5-m height from the soil surface and the measurements were performed at a 10-Hz sampling rate. We used the eddy covariance technique for determining the CO2 fluxes. With this method, we can determine the vertical CO2 fluxes from the correlation between the temporal high-frequency deviations of vertical Wind speed with the deviations of the temporal scale. The application of eddy covariance is based on the assumption that the eddy, while advected through the sensor, for a stationary and homogeneous flow, maintains its properties unaltered (Taylor hypothesis). Key words: carbon dioxide, flux, eddy covariance.