Analysis of small-scale soil CO₂ fluxes in an orange orchard under irrigation and soil conservative practices

The quantification of soil carbon dioxide (CO₂) flux represents an indicator of the agro-ecosystems sustainability. However, the monitoring of these fluxes is quite challenging due to their high spatially-temporally variability and dependence on environmental variables and soil management practices.In this study, soil CO₂ fluxes were measured using a low-cost accumulation chamber, that was realized ad hoc for the surveys, in an orange orchard managed under different soil management (SM, bare versus mulched soils) and water regime (WR, full irrigation versus regulated deficit irrigation) strategies. In particular, the soil CO₂ flux measurements were acquired in discontinuous and continuous modes, together with ancillary agrometeorological and soil-related information, and then compared to the agrosystem scale CO₂ fluxes measured by the eddy covariance (EC) technique.Overall significant differences were obtained for the soil CO₂ discontinuous fluxes as function of the WR (0.16 ± 0.01 and 0.14 ± 0.01 mg m^-2 s^-1 under full irrigation and regulated deficit irrigation, respectively). For the continuous soil CO₂ measurements, the response observed for the SM factor varied from year to year, indicating for the overall reference period 2022-23 higher soil CO₂ flux under the mulched soils (0.24 ± 0.01 mg m^-2 s^-1) than under bare soil conditions (0.15 ± 0.00 mg m^-2 s^-1). Inter-annual variations were also observed as function of the day-of-year (DOY), the SM and their interactions, resulting in higher soil CO₂ flux under the mulched soils (0.24 ± 0.02 mg m^-2 s^-1) than under bare soil (0.15 ± 0.01 mg m^-2 s^-1) in certain periods of the years, according to the environmental conditions.

suggest the importance of integrating soil CO₂ flux measurements with ancillary variables that explain the variability of the agrosystem and the need to conduct the measurements using different operational modalities, also providing for night-time monitoring of CO₂. In addition, the study underlines that the small-scale chamber measurements can be used to estimate soil CO₂ fluxes at orchard scale if fluxes are properly scaled.