Addition of compost changed responses of soil-tree system in olive groves in relation to the irrigation strategy

Intensification of olive production could suppose an increase of natural resources consumption as well as an acceleration of soil degradation. Studies of soil and trees combining different strategies of water management and fertilization to solve these drawbacks are scarce and contradictory. The aim of this work was to describe the effect of organic and inorganic fertilization in soil parameters (water availability, physico-chemical properties and greenhouse gas emissions) and tree development (fruit and crown growth pattern) in rainfed and irrigated conditions in two different olive systems (hedgerow and intensive). The solid olive-mill by-product called "Alperujo" compost (AC) was added as organic fertilization in both systems and two irrigation managements (full and deficit) at the hedgerow sites were also considered. The addition of AC tended to increase soil water retention and soil organic matter (SOM), displaying on average about 15% and 20% more respectively in soils treated compared to their controls in both experiments. Irrigation rather than compost addition was the factor controlling the evolution of both fruit and tree growth. However, AC seemed influenced fruit production specially at the hedgerow system that yielded 30% and 41% more for the deficit and full irrigation management with compost than their respective controls. Emissions of GHE did not generally increase with the AC addition and showed a marked seasonal character in both sites. Regardless irrigation, at the hedgerow site, the full irrigation regimen tended to increase CO2 and CH4 soil fluxes. The agronomic use of organic wastes combined with a deficit irrigation strategy proved to be an efficient tool for nutrient recycling, and promoting a zero waste circular economy and a water conservation strategy.