Soil survey in irrigation investigations [antikvár]

- V - SOILS BULLETIN : SOIL SURVl^Y B^ IHRIGATIOW IKVESTIGATIONS FOHBVJORD Even the most optimistic muut recognize the pressing need for increased afp:'icultural production in the years ahead and for more efficient use of our finite resources of land and of water. Only by better and more widespread use of irrigation can the needed j -'oduotion increase be achieved in those huge areas of the world where rainfall is :;iadequate or uncertain. Production gains from the expansion and intensification of irrigated agriculture will be shortlived, however, if the attendant hazards of salini-sation and waterlogging are not kept in check through sound planning and management based upon thorough understanding of the available soils. Soil survey and land classification are generally accepted to be essential preliminaries to large scale investment in irrigation development. However, many of the classical techniques and procedures of soil survey have "been developed in temperate areas with the requirements of rainfed agriculture predominantly in mind. Understandably, these methods may not be ideal for the survey of potentially irrigated areas for, where moisture is in short supply, different criteria require emphasis in assessing the agricultural potential of land and corresponding differences in emphasis are needed in the investi-f^ations involved. It is the aim of this document to describe these differences with a 'dew to enhancing the contribution of soil survey work to irrigation investigations of all kinds. Throughout the document the reader is assumed to have a sound knowledge of soil science and of general soil survey technique. No book on soil survey can be an effective substitute for experience gained in the field but this document attempts to highlight the soil characteristics which are most significant in their influence on soil behaviour under irrigation and to suggest ways in which the local expression of these characteristics can be recognized and mapped, lie opening chapter emphasizes the breadth of the considerations involved in evaluating land for irrigation and describes the role of the soil surveyor in the required team of specialists. The chapter continues with a summary of the features that distinguish soil surveys of potentially irrigated land and concludes with some notes on the planning of these surveys. The characteristics of soils and of topography which are most significant in determining land suitability for irrigation are discussed individually in the next two chapters. Chapter Pour describes the assessment of soil drainage and soil reclamation possibilities and Chapter Five considers the relevance of water quality and climate to irrigation suitability of land. Field methods of soil survey are reviewed in Chapter Six whilst, in Chapter Seven, various stages of data interpretation suited to different objectives and conditions of survey are described. Two appendices are included in the document. The first presents a number of examples of land class specifications, prepared for different environments. The second appendix describes procedures for the field measurement of permeability oxid infiltration. The present draft of the document has been prepared with the most generous help of the Bureau of Reclamation of the U.S. Department of the Interior. It is a great pleasure to have this opportunity to express to the staff of the Division of Planning Coordination at the Engineering and Research Center, Denver, my appreciation of the unstinting assistance which they have extended in this work.