Water Related Properties to Assess Soil Quality in Two Olive Orchards of South Spain under Different Management Strategies

Soil quality is usually assessed through the measurement of selected soil properties. However, in spite of the diversity of the chosen properties, use of the soil water retention curve, like the pressure head or the specific water capacity at the inflection point, provides relevant information of degradation or improvement of soil. The main aim of this study was to evaluate the methods based on these indices in the evaluation of short-term changes of olive cropped soils under typical Mediterranean agricultural conditions. For this reason, soil properties (bulk density, hydraulic conductivity, aggregates stability, and organic matter content) were measured in a short-term trial settled in two olive orchards under different soil managements: tillage and cover crop. Several sampling areas were also distinguished: (i) along the inter tree row and under the canopies’ projection and (ii) at 0–10 cm and 10–20 cm depth. In addition, water retention curves were determined and fitted using two models (van Genutchen’s and Kosugi’s) in order to obtain the inflection point and therefore the S index. This index is the maximum value of the slope of the soil water retention curve and is related to soil quality. At the two sites, changes in soil management, even after a brief period of two years, had a relatively quick effect, especially in organic matter content along the inter tree row. The use of indices based on soil water retention curves helps to detect soil degradation or improvement changes. Future research, including the inclusion of more soil types and longer time periods, might lead to the development of more refined tools for the assessment of soil health.