This study is based on the work of John Ryan, Soil Fertility Specialist/Technical Editor, Natural Resource, Management Program (NRMP), International Center for Agricultural Research in the Dry Areas (ICARDA) Syria and Ahmed Mazid of the same centre.
The study benefited from the contributions of K. Isherwood, J. Poulisse and T. van den Bergen (FAO).
The cover photographs were provided by Arnoldo Montadori Editore S.p.A. (grapes) and J. Ryan (safflower and barley). The background photograph (wheat) was provided by FAO/ 18650/G. Blaak.