302 ELEMENTS OF GENERAL SCIENCE 



it is led off through ditches to the fields. In case of rivers 

 which flow through flat valleys the water is sometimes 

 pumped into irrigation ditches or into elevated reservoirs. 



305. Dry farming. In some parts of the United States 

 there is an amount of rainfall which would give the soil 

 sufficient water to produce a crop if evaporation could be 

 prevented. In some such regions the experiment has been 

 tried of keeping the soil under surface cultivation for a long 

 time. First, deep plowing is done, furnishing a deep soil for 

 the absorption of rainfall. Then constant surface cultivation 

 retains most of the moisture, and after a time enough moisture 

 may thus be caught and held to make it possible to grow a 

 crop. In some cases where this type of farming is done the 

 rains are so scanty that a crop can be grown only once in 

 two years. Possibly some water may be drawn upward from 

 the deep soil, but most of it must come from the scanty and 

 infrequent rains. 



It is evident that dry farming requires much labor in order 

 to put the soil in proper condition for the production of a 

 crop. Even with these difficulties fine crops have been grown 

 by dry farming, and when we consider the extreme cheapness 

 of land in the dry-farming regions, the relative amount of 

 labor seems well repaid in results. Dry farming is still 

 somewhat in the experimental stage, and whether it is to be 

 extended to cover other large areas where there is scanty 

 rainfall cannot be safely predicted. In any event, there are 

 large areas of dry land which receive no ram, or practically 

 none, and these areas must look to some form of irrigation 

 to make them productive. The quantity and availability of 

 the water supply have thus far limited irrigation to relatively 

 small areas, though the total acreage seems large. Whether 

 the Great American Desert is to be obliterated and become a 

 highly fertile region is largely a question of the quantity and 

 availability of water. There may be sources of water supply 

 (from deep wells or from the ah-) not yet within the range of 



