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The olive tree is one of the most important crops in Spain, and the main one in the region of Andalusia. Most orchards are rain-fed, with high slopes where conventional tillage (CT) is the primary soil management system used. These conditions lead to high erosion and a significant transport of organic carbon (OC). Moreover, soil tillage accelerates the oxidation of the OC. Cover crops (CC) are the conservation agriculture (CA) approach for woody crops. They are grown in-between tree rows to protect the soil against water erosion and their organic residues also help to increase the soil carbon (C) sink. Soil and OC losses associated to the sediment were measured over four seasons (2003-07) using micro-plots for the collection of runoff and sediment in five experimental fields located in rain-fed olive orchards in Andalusia. Two soil management systems were followed, CC and CT. Furthermore, the changes in soil C in both systems were analyzed at a depth of 0-25 cm. CC reduced erosion by 80.5%, and also OC transport by 67.7%. In addition, CC increased soil C sink by 12.3 Mg ha -1 year -1 of carbon dioxide (CO 2 ) equivalent, with respect to CT. Cover crops in rainfed olive orchards in a Mediterranean climate could be an environmental friendly and profitable system for reducing erosion and increasing the soil C sink. However, C fixing rate is not regular, being very high for the initial years after shifting from CT to CC and gradually decreasing over time.

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The spatial characterization of soil protection is important for preventing land degradation. Mulch covers of pruning residues are increasingly used by farmers, but little is known regarding their spatial variability. Thus, field research was conducted in a 14·7‐ha traditional olive grove located in Córdoba (Spain), to evaluate the variability of the initial density of pruning (Dpo), tree crown volume (V) and N content in residues (Np). Dry pruning weight and Np were characterized in 49 and 47 samples, respectively, covering approximately half of the area. V was measured in 178 locations covering all of the study area. The spatial continuity of these variables was described by spherical variograms. Geostatistical simulation algorithms were employed. One hundred realizations were made for Np through direct sequential simulation. Because the association with V was large (rxy = 0·72, p‐value < 0·001), we ran a geostatistical cosimulation algorithm to obtain 100 maps of Dpo. The final density of pruning (FDp) was determined by applying a residue decomposition model for a 2‐year period to pairs of previously simulated maps of Np and Dpo. After setting soil protection cut‐off values for FDp, the soil protection probability was calculated for pruning strips of 2 and 4 m width. Finally, we converted the probability maps into binary maps and classified the farm into protected, unprotected and uncertain zones. V provided valuable input to evaluate soil protection. The application of stochastic simulations coupled with a decomposition model was useful to identify critical areas. This methodology can be easily applied to other crops. Copyright © 2017 John Wiley & Sons, Ltd.