Selecting indicators for assessing soil quality and degradation in rangelands of Extremadura (SW Spain)

Abstract

Spanish rangelands are considered to be of high nature value and a habitat of interest in the European Union due to their productivity and species diversity. However, they are fragile landscapes where farmers’ decisions, such as changes in livestock pressure, can lead to serious deterioration. Currently, no indicator system is being used in these areas to enable farmers to evaluate the condition of rangeland soils. Aiming at this, soil properties, land degradation processes, rainfall characteristics, as well as pasture and land management were analysed in order to propose a set of soil quality and degradation indicators. The study was carried out on 22 enclosures selected from 10 privately-owned farms distributed throughout the Spanish region of Extremadura. Cation exchange capacity, available potassium, soil organic matter, water content at field capacity, soil depth and the thickness of the Ah-horizon were selected as soil quality indicators, with the percentage of bare ground cover and bulk density measured from 5 to 10cm in depth selected as soil degradation indicators. All the indicators were classified into 5 categories and land units were assessed accordingly. The results revealed that 14% of cases showed very low soil quality and 18% high degradation. The reasons that motivated the selection and categorisation of each indicator are described and the proposed system is compared with other existing indicator systems.