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Losses of soil organic carbon (SOC) have contributed to CO2 emissions from soils to the atmosphere and to global climate change. We hypothesized that in semiarid agroecosystems of the Mediterranean region, a shift from the traditional management system (including conventional tillage [CT] and a cereal-fallow rotation) to a more conservative system, including no-till (NT) and continuous cropping, could reduce CO2 emissions during the cropping season. Thus, in this study, we studied the effects of tillage and cropping systems on C inputs and soil CO2 fluxes during three cropping seasons at three different sites in the Ebro River valley (northeast Spain). Carbon inputs ranged from 650 to 6000 kg ha-1 and seasonal average CO2 flux ranged from 0.10 to 1.76 g CO2 m-2 h-1. Differences in rainfall led to marked differences in C inputs and soil fluxes among growing seasons. Although differences among tillage treatments were weak, CO2 fluxes under NT were always lower. Intensification of cropping systems led to an increase in C input. A move from CT to NT together with cropping intensification is suitable to increase C inputs and to reduce soil CO2 fluxes in semiarid Mediterranean agroecosystems. [ABSTRACT FROM AUTHOR]

During the second phase of the European International Project on Climatic and Hydrological Interactions between Vegetation, Atmosphere, and Land Surface (ECHIDA) Field Experiment in a Desertification Threatened Area (EFEDA) the spatial variability of the soil water retention and hydraulic conductivity characteristics of layers at 2–12- and 17–27-cm depth was characterized. A simplified method, based on particle size distribution and simple infiltration tests, was used. It provided these characteristics at the nodes of a 1-km grid over 10 × 10 km[sup 2] around the town of Tomelloso (Castilla–La Mancha, Spain). A total number of 78 sample points were used to address the problem of soil surface properties variability and its consequences on the monthly and annual water balance. The Simple Soil Plant Atmosphere Transfer model (SiSPAT) 1D Soil–Vegetation–Atmosphere Transfer (SVAT) model was run with a 1-yr climatic forcing for the 78 soil profiles until equilibrium was reached. As no runoff was generated, the spatial variability of the water budget components only concerned soil evaporation, transpiration, and deep drainage. It was found that (i) the choice of the type of boundary condition at the bottom of the soil profile was greatly influencing the final variability, (ii) the variability of transpiration was the largest in situations of water stress for the vegetation, and (iii) soil evaporation was the most sensitive component when plants were well supplied with water. Various aggregation methods of soil surface parameters (use of the arithmetic mean, median of the parameters, or parameters associated to the average soil texture of the Clapp and Hornberger classification) were assessed. The use of median parameters in a single 1D simulation was found to provide the best agreement with the average of the 78 simulations performed for each grid cell using locally measured soil properties. The use of average soil texture... [ABSTRACT FROM AUTHOR]