IRRIGATION AND DRY FARMING 173 



The furrows should usually be run off from three to eight 

 feet apart, depending, of course, on the nature of the soil, 

 that is, as to its readiness to soak up water. This may easily 

 be determined by experiment before the furrows are laid 

 out. After the water has been shut off from the furrow and 

 the surface has become dry enough, the furrow should be 

 filled again to prevent too rapid evaporation. Losses due 

 to this cause often amount to as much as 50 per cent of the 

 water applied. Experience has proved that wide and deep 

 furrows are much better than narrow and shallow ones. 

 Where the former are used, it is possible to fill the furrows 

 much sooner after irrigation, thus preventing great loss by 

 evaporation, and the water also sinks to a greater depth in 

 the soil, thus rendering it unnecessary to apply the water 

 so often. 



Dry Farming. In the semiarid regions of the western 

 part of the United States, where the rainfall for the entire 

 year is not enough to mature a crop, a system of cultivation 

 known as " dry farming " is coming to be practiced more 

 and more. It should not be inferred from the name that 

 by the practice of this system plants are able to thrive on 

 smaller quantities of water than in other cases. The system 

 consists in carefully preserving the moisture which falls dur- 

 ing an entire year. During this year the land is riot sowed to 

 crops, but is so treated as to permit of a very small amount 

 of evaporation. The surface is constantly kept loose, being 

 stirred after each rain of any considerable amount. Before 

 planting, a machine called a subsurface packer is run over 

 the ground. This machine consists of a number of wheels 

 placed five inches apart on a shaft, each wheel being eighteen 

 inches in diameter. The rim of each wheel is one inch thick 



