Olive Cultivation, its Impact on Soil Erosion and its Progression into Yield Impacts in Southern Spain in the Past as a Key to a Future of Increasing Climate Uncertainty

This article is intended as a review of the current situation regarding the impact of olive cultivation in Southern Spain (Andalusia) on soil degradation processes and its progression into yield impacts, due to diminishing soil profile depth and climate change in the sloping areas where it is usually cultivated. Finally, it explores the possible implications in the regional agricultural policy these results might have. It tries to show how the expansion and intensification of olive cultivation in Andalusia, especially since the late 18th century, had as a consequence an acceleration of erosion processes that can be identified by several indicators and techniques. Experimental and model analysis indicates that the rate of soil erosion accelerated since the expansion of mechanization in the late 1950s. In addition, that unsustainable erosion rates have prevailed in the region since the shift to a more intense olive cultivation systems by the end of the 17th Century. Although agroenvironmental measures implemented since the early 2000s have reduced erosion rates, they are still unsustainably high in a large fraction of the olive area in the region. In the case of olive orchards located in steeper areas with soils of lower water-holding capacity (due to coarse texture and stone content), cumulative erosion has already had a high impact on reducing their potential productivity. This is one of the factors that contributes towards increasing the gap between these less intensified orchards in the mountainous areas and those in the hilly areas with more gentle slopes, such as for instance the lower stretches of the Guadalquivir River Valley. In the case of olive orchards in the hilly areas with better soils, easier access to irrigation and lower production costs per unit, the efforts on soil conservation should be oriented towards limiting off-site damage, since the soil water-storage function of these soils may be preserved in the medium term even at the current soil erosion rates. The assessment made in this manuscript should be regarded as an initial approximation, since additional efforts in terms of increasing experimental records (for current or historical erosion) and of improving model analysis, with more comprehensive studies and more robust calibration and validation processes, are required.

This study has been made possible by contributions from different research projects, including P08-AGR-03925 (Andalusian Government), AGL2009-12936-C03-01 (Spanish Ministry of Science and Innovation), AGL2012-40128-C03-01, and AGL2012-40128-C03-02 (Ministry of Economy and Competitiveness) and FEDER funds. Tom Vanwalleghem acknowledges funding by the Spanish Ministry of Economy and Competitiveness (through the Ramón y Cajal Fellowship RYC-2010-07166). We would also like to thank one anonymous reviewer, whose help and careful revision has greatly contributed towards improving the quality of our study.

We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).