2. Water Management for Irrigation 



Only about one-seventh of the world 1 s 1.4 billion 

 hectares of cropped land is irrigated, but in terms of 

 value these lands produce almost as much food as all 

 nonirrigated lands (Kovda 1971, NRC 1977:66-67). 

 Irrigation makes it possible to produce crops or gain 

 higher yields on lands otherwise too arid, to extend 

 growing seasons and to increase the prospects for 

 multiple cropping in wet-dry climates, and to insure 

 against short-term droughts during abnormal seasons. 



Heavily populated areas of developing countries 

 essentially have no new lands to bring under 

 cultivation, so that intensification of farming is 

 essential if enough food is to be produced. For 

 example, production of rice seldom rises beyond 1.5 

 tons per hectare without irrigation (Takase and Kano 

 1969:513-551); with it, this figure can usually be 

 doubled. Moreover, water control can increase the 

 impact of other inputs such as fertilizer and pest 

 management, which are otherwise of little value. Such 

 practices as soil management, crop and variety 

 selection, fertility interactions, pest and weed 

 control, seeding methods and rates all influence yields 

 and are important before production can reach full 

 potential in an irrigation system. For example, the 

 combination of water control and other modern inputs 

 can result in rice yields of 7 tons per hectare and up. 



The situation is similar for upland crops grown 

 under irrigation. If irrigation is employed in wet-dry 

 tropical, subtropical, and even temperate areas, two or 

 three crops can be grown where only one would otherwise 

 be possible. 



Rationale for Selecting this Topic 



Irrigation is a major area for capital investment 

 in the developing countries, where there are already 

 some 92 million hectares of irrigated land. Yet 

 investments in irrigation have often failed to pay off 

 as planned. Increases in yields fall far short of 

 expectations and waterlogging and salinity too often 

 accompany irrigation. The principal reason for these 

 deficiencies is that the delivery of water to the 

 fields and the distribution of water on the fields are 

 remarkably inefficient, both physically and in terms of 

 management. Water is not delivered when it is needed, 

 and as much as 75 percent is wasted. Not only is this 

 inefficient, but it is a major cause of waterlogging 

 and salinity. The basic capability to diagnose and 

 correct this difficulty is available. Therefore, we 

 propose an accelerated program to help improve farm 



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