## Results
### CenW Performances to Simulate Carbon Dioxide and Water Fluxes of Mown and Grazed Grasslands
#### 3.1.1 Carbon Dioxide Fluxes  
Comparisons between modeled and measured daily CO\({}_{2}\) fluxes for the two differently managed grasslands are shown in Figure 3, and model efficiencies for model calibration and validation are given in Table 1. In this section, only the best quality data from background periods (outside mowing and grazing events) were used for the comparisons. Observations that would have been affected by mowing and grazing events were omitted from the analyses [56], as well as days when fluxes from the eddy covariance systems had to be gap filled for more than 1/3 of half hourly periods. This selection of only best quality observation was necessary to avoid  
1. the calibration of the model with data that strongly depended on another simpler model (i.e., the Reichstein gap-filling and partitioning tool) and
2. to limit the bias that would have resulted from the non or incomplete capture by EC of the large respiratory losses during measurement periods when grazing animals were present around the EC tower or when freshly cut or drying grass was present on the ground during moving events [56; 79]. For the NEE dataset, which was separated into parameterization and validation subsets, R\({}^{2}\), and model efficiencies are slightly higher for the parameterization subset than for the validation one for the two grassland sites. Moreover, in general, model/data agreements (Figure 3 and Table 1) are better for GPP and ER than for NEE as it is easier to model large photosynthesis and respiration fluxes \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Mowed Paddock**} & \multicolumn{3}{c}{**Grazed Paddock**} \\ \hline  & & **Daily** & \multicolumn{3}{c}{**Weekly**} & \multicolumn{3}{c}{**Daily**} & \multicolumn{3}{c}{**Weekly**} \\ \hline  & **Calibration** & **Validation** & **Total** & **Total** & **Calibration** & **Validation** & **Total** & **Total** \\ \hline
**GPP** & - & 0.85 & 0.85 & 0.87 & - & 0.80 & 0.80 & 0.79 \\
**ER** & - & 0.77 & 0.77 & 0.78 & - & 0.72 & 0.72 & 0.67 \\
**NEE** & 0.75 & 0.73 & 0.74 & 0.72 & 0.64 & 0.66 & 0.65 & 0.64 \\
**ET** & 0.82 & 0.81 & 0.82 & 0.87 & 0.81 & 0.80 & 0.85 \\
**Averaged SWC** & - & 0.85 & 0.85 & 0.87 & NA & NA & NA & NA \\
**Harvested** & - & 0.80 & - & NA & NA & NA & NA & NA \\
**biomass** & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Model efficiencies for six key observations of the two-modeled systems. Only daily NEE and ET were used for the model parameterization. ‘Total’ refers to the complete data set that included data in both the parameterization and validation data sets. than the relatively small difference between the two (NEE). Model/data agreements are also better for moving than for grazing, certainly because of the higher complexity of grazed systems compared to moving. On the one hand, for the mowed paddock, management practices (moving events and fertilizer applications) are accomplished within a day and evenly applied to the field. While, on the other hand, for the grazed paddock, grazing events last several consecutive days, the stocking density vary for the different events, there are dung and urine patches, there is an uneven reparation of cattle on the paddock, there could be some preferential grazing of plant species, and pasture could be damaged by trampling. Figure 3: Scatter plots of observed vs. modeled daily carbon fluxes for the mown (panels **a–c**) and grazed (panels **d–f**) paddocks, for background measurement periods outside management (grazing, mowing) events. For NEE, negative numbers refer to carbon gain by the system. Corresponding model efficiencies for each comparison are given in Table 1.  
After parameterizing the model with good quality data over the full length of the study period (2006-2010), we obtained good agreement between modeled and observed carbon fluxes. Figure 3a,b shows the comparison of daily modeled GPP against their observation-based counterparts for the moved and grazed paddocks, respectively.