SUMMARY
The combined impact of soil tillage intensification and expansion of olive farming is resulting in soil degradation and biodiversity decline. We hypothesized that, instead of tilling, mowing to control the natural vegetation in spring can increase biodiversity and improve soil quality. We compared the effects of natural vegetation mowing (NVM) with those of tillage (NVT) on plant community composition and cover, soil water content and resistance to penetration, and olive yield over an 8-year period, in a Mediterranean rainfed olive orchard. NVM had an average of 28 more species and showed a strong positive correlation with Poaceae and Fabaceae, and also with geophytes and hemicryptophytes. In contrast, NVT was negatively correlated with species richness and diversity, with perennial life forms, and positively correlated with Convolvulaceae. Proportions of grass and straw cover in spring were higher in NVM from the beginning of the study (average difference was about 20%). In autumn, grass cover became higher in NVM than in NVT from year five (13% more) and straw cover from year two (30% more). Olive production did not differ between treatments in any of the years. Soil water was higher in NVM, at both soil depths, particularly in mid-summer and after the first autumn rains (1 to 2%). Soil resistance to penetration was 1 Mpa higher in NVM than in NVT. As compared to conventional tillage, natural vegetation cover mowed in spring seems to be an effective management practice to improve the overall rainfed olive orchard biodiversity and soil quality, without affecting production.