1. Soil and Water Science Dept., Faculty of Agriculture, University of Alexandria, El‐Shatby, 21545 Alexandria, Egypt
2. LUFA Speyer, Obere Langgasse 40, D‐67346 Speyer, Germany
3. Institute of Plant Nutrition, University of Hannover, Herrenhäuser Str. 2, D‐30419 Hannover, Germany