Abstract
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, Cover crops increased soil C sink by 12.3 Mg ha-1 year-1 of carbon dioxide (CO2) equivalent, with respect to CT. CC 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.
Highlights
Olive trees (Olea europaea L.) are native to the Mediterranean basin; it is in Spain where they have reached their greatest development and implantation (Civantos, 2008)
Differences were observed in the textures of the experimental fields and especially in the organic carbon (OC) content, which was influenced by the granulometric composition of the soil, the weather and the different tillage systems used by the olive grower
Average bulk density increased by 4% with the Cover crops (CC) system, whereas bulk density was distributed more homogeneously under the conventional tillage (CT) system
Summary
Olive trees (Olea europaea L.) are native to the Mediterranean basin; it is in Spain where they have reached their greatest development and implantation (Civantos, 2008). Most plantations are rain-fed, occupying 74.5% of the total olive cultivated area in Andalusia (CoAP, 2003) and are normally grown on relatively poor soils with steep slopes. 18% are found on slopes of less than 5% (CoAP, 2003) These facts, together with a Mediterranean climate with lengthy periods of drought followed by frequent torrential storms, result in high soil losses as intensive tillage is the most common soil management system (Pastor, 2004; Gómez, 2005; Vanwalleghem et al, 2010).
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