**Acknowledgements**

I wish to express my deepest gratitude to:Friends: Dr Youssef Gamtey Benghazi University,for his assistance and guidance in statistical.To Mrs Susan McCourt of the Queen Mother Library, University of Aberdeen, for her assistance and guidance in the use of the Refworks software and to Mrs Alison Sage for her copy editing. Libyan Agricultural Projects (Aril, Maknowsa, Tasswat, Bengzh, Darna Srit and Sluq) for soil and plant sampling.
