DRAINAGE, IRRIGATION, AND DRY FARMING 125 



Irrigation is sometimes practiced in humid regions with a rain- 

 fall of from thirty to forty inches, but this is usually profitable 

 only under systems of intensive farming or where the crops 

 have a high market value. Lands grown to truck crops come 

 in this class, while in certain parts of Europe, where hay is high 

 priced, meadows are profitably irrigated. 



152. How water is applied. Water is usually brought to the 

 land in canals from streams or lakes and distributed over the 



FIG. 52. Irrigating in California 



The side, or lateral, ditches carry the water from the supply ditch to the trees. (Photograph 

 from Office of Experiment Stations, United States Department of Agriculture) 



fields in small ditches (Fig. 53). If the crop is one which cov- 

 ers the surface of the ground, such as clover, wheat, or alfalfa, the 

 field is usually flooded. Rice is grown on lands which can be 

 kept covered with water during the first part of the crop's growth 

 (Fig. 54). Where crops are grown in rows and cultivated, the com- 

 mon plan is to run the water down the furrows between the rows 

 and allow it to enter the soil from the furrow. Under special 

 systems of cropping, overhead pipes are installed and the water 

 is sprinkled on the soil in a manner resembling the fall of rain. 



