Some fifty million hectares of land could be developed for irrigated agriculture in the next twenty-five years. An even larger area needs rehabilitation or changes connected to intensified production. Irrigation developments are expensive and usually require investment and credit facilities, and mistakes are very costly. Therefore, almost all of this vast area will need to be evaluated to ascertain its suitability for the proposed irrigation systems.
The Land and Water Development Division of FAO has been concerned with land development for many years and has developed methods of assessing the suitability of land for specific uses so that reliable predictions and recommendations can be made (FAO 1976).
Irrigation is a major kind of land use with special requirements. So guidelines are needed to ensure that the methods adopted for evaluating and classifying land suitability are adequate. They are intended to provide guidance to land classification teams in the field and also to agencies responsible for investing in irrigation development so that they can make sure that the land resources evaluation provides a satisfactory basis for predicting the results of development.
This document is the result of collaboration among many specialists. An expert consultation recommended its production (FAO 1979) and a draft prepared by the USBR was discussed in 1983 by representatives of the World Bank, US Bureau of Reclamation (USBR), FAO and others. This provided the basis for a second draft prepared by consultants, Dr. B. Eavis (Land Resources Development Centre, U.K.) who wrote the main body of the report, and Dr. R. Struthers (formerly of the USBR), in consultation with Mr. M.F. Purnell and other staff members of FAO. The draft was circulated widely and numerous suggestions were incorporated in this version. FAO would like to thank all those who have contributed.
The procedures described are not intended as formal instructions but as optional guidelines to assist people to improve their own evaluations of their land and water resources. Likewise, the critical limits for land classes suggested in Part Two are guides which must be adapted to local circumstances. Comments and suggestions on their applicability, which will enable a future re-issue to be amended in the light of experience, should be sent to the Land and Water Development Division of FAO.