Net ecosystem CO2 exchange in an irrigated olive orchard of SE Spain: Influence of weed cover

No-till management and the establishment of plant cover have been implemented in olive crops in recent years in order to prevent soil erosion and increase soil organic carbon. However, the effect of these conservation practices on the net CO2 exchange at the ecosystem scale has not been explored so far. In this study, we analyze the influence of resident vegetation cover (hereafter weeds) on the net ecosystem CO2 exchange (NEE) in an irrigated olive orchard located in Jaén (SE Spain) by using the eddy covariance technique. NEE was measured in the olive orchard under two treatments, one with weed cover in the alleys from autumn to spring, and another where weed growth was avoided by the application of a glyphosate herbicide. Our study demonstrates that the presence of weeds in the alleys increased carbon assimilation in the weed-cover treatment during the weed growing period (from December to April). However, the net ecosystem CO2 uptake decreased in the weed-cover treatment during late spring (May and June), after weeds were cut and left on the soil, compared to the weed-free treatment, probably due to an increase in soil respiration. On an annual basis, weed removal decreased net carbon uptake by 50% compared to the weed-cover treatment. The annual NEE was −140 g C m−2 y−1 in the weed-cover treatment and −70 g C m−2 y−1 in the weed-free treatment. In summary, our study demonstrates that, during the first year of differential treatment, maintenance of weed cover in olive groves has a positive effect on CO2 uptake and enhances the capacity of the agro-system to act as a net CO2 sink.

This work was funded by the Andalusian Regional Government (Ministry of Innovation, Science and Business) project CARBOLIVAR (P11-RNM-7186), the Spanish Ministry of Economy and Competitiveness project GEISpain (CGL2014-52838-C2-1-R), both including ERDF funds, and also by the international project DIESEL (PEOPLE-2013-IOF-625988). We thank Roberto García for help in soil sampling and Eva Arnau for help in preparing the figure of the study site. Special thanks are given to the Group Castillo de Canena for the use of their farm as an experimental site and for continuous cooperation in the development of the project. We thank the editor and two anonymous reviewers for their constructive comments that have helped improve the quality of this work.

Peer reviewed