1. Ethiopian Institute of Agriculture Research; Holetta Agri. Research Center; P.O. Box. 2003 Addis Ababa Ethiopia
2. Area of Soil Science and Soil chemistry; E.T.S. Ingenierías Agrarias; University of Valladolid; Avda. de Madrid 57 34071 Palencia Spain
3. Department Vegetable Production and Forest Resources; University of Valladolid; Avda. de Madrid 44 34004 Palencia Spain
4. Sustainable Forest Management Institute; University of Valladolid-INIA; Avda. de Madrid 44 34004 Palencia Spain