## 3 Results and Discussion
### The Fluxes of CO\({}_{2}\) and H\({}_{2}\)O  
The trends of hourly EC fluxes Fc and Fq for the watermelon crop are reported in Figures 4 and 5, respectively; the patterns are illustrated at a decadal scale to capture the dynamics during the entire experimental period. During the first month after planting (June), Fc was always positive due to bare soil respiration, with values decreasing from the first to the third decade as vegetation  
Figure 3: Patterns of leaf area index (LAI) and fresh biomass (FB) measured during the crop growth cycle. The error bars represent the standard deviations, shown for clarity only in one direction. Figure 2: The soil water content (\(\theta\)) daily trend in the experimental period (1 June–30 November 2023). The horizontal green and red lines indicate the field capacity and the wilting point, respectively; irrigation and precipitations are also reported. developed, increasing LAI and FB and enhancing CO\({}_{2}\) assimilation (Figure 3). During July and August, when the crop was fully developed, the system acted as a complete carbon sink during daytime, reaching maximum values from \(-15\) up to \(-20\) umol m\({}^{-2}\) s\({}^{-1}\) in the third decade of July. In the third decade of August, during the scalar harvest of the fruits, the system became a weak carbon sink, gradually turning into a carbon source from September until the end of the experiment. In early November, a small CO\({}_{2}\) assimilation likely resulted from weeds grown in the field before tillage for the successive crop. During nighttime, the system was always a very weak source of carbon. The patterns of Fq (Figure 5), always at a decadal scale, followed the standard actual crop evapotranspiration trend throughout the experimental period. The only deviation from the standard ET trend can be seen in the third decade of September, when heavy rainfall (Figure 1) supplied water to the soil, which was available for evaporation. This feature can also be partially attributed to the inclusion of fresh chopped biomass rich in fully available water to the soil [57]. The maximum Fq values (around 8 mmol m\({}^{-2}\) s\({}^{-1}\)) were reached in the third decade of July through the first decade of August, corresponding with the highest Fc values (see Figure 4). Furthermore, the Fq trend was very similar in the first and second decades of September, when a decrease in evaporation would have been expected in the absence of rainfall and irrigation (see Figure 1). The partitioned fluxes of CO\({}_{2}\) and H\({}_{2}\)O are presented at a daily scale for the entire experimental period in Figures 6 and 7 for the stomatal and non-stomatal components, respectively; surface coverage is also shown in both figures. Figure 5: The trends of hourly eddy covariance water vapor fluxes (Fq) from June to November are presented in panels (**a**) through (**f**). Fq patterns are reported at a decadal scale in the whole experimental period (June–November 2023) of watermelon crop. Figure 6: Stomatal fluxes (transpiration and photosynthesis) at daily timescale as partitioned by the FVS method during the growth seasons; the surface covering is also reported. The trends of plant transpiration and photosynthesis were naturally opposite (Figure 6), aligning perfectly with canopy development as indicated by coverage, from the beginning of the growth season until residual chopping in early October. Afterward, both transpiration and photosynthesis ceased until the end of the experiment. The soil evaporation and respiration (Figure 7) followed the typical trend of a well-irrigated crop; however, in this case, the CO2 emissions from the soil presented quite high values a few days after harvesting of watermelon fruits and, further, after the residual chopping. This pattern was also reported for evaporation, even if with less evidence.