1. Department of Soil Science and Agricultural Chemistry, Escuela Politécnica Superior, University of Santiago de Compostela, E–27002 Lugo, Spain
2. Department of Plant Biology and Soil Science, Faculty of Biology, University of Vigo, E–36200 Vigo, Spain
3. FISQUITECNAL, Faculty of Sciences, University of Santiago, E–27002 Lugo, Spain