ABSTRACT
The humus content of some soils may decrease after a period of irrigation or the installation of drainage and this dehumification may alter the soil nutrient status and structure. Sometimes groundwaters are contaminated by agro-chemicals, salts or disease organisms from sewage effluent applied to irrigated fields. Irrigation-caused Stalinization is widespread, very important and by no means restricted to developing countries or the tropics. Climatic impacts seem likely that large irrigation projects, particularly in arid regions, can affect local, and possibly regional, climates by altering the albedo of the area cropped. Fish and other edible organisms usually colonize irrigation channels and padi-fields and, provided these are not contaminated with agrochemicals, they can provide a valuable source of food for man and wildlife. Both malaria and schistosomiasis, and many other irrigation-related diseases, must be dealt with using an integrated approach combining drugs, health education, sanitation, disease-avoidance engineering and a sound understanding of the nature of the disease.
