58 IRRIGATION PRACTICE 



irrigated soils. However, in practice it is often difficult 

 to cultivate below a depth of approximately 6 inches, 

 unless the soil is of the right character and proper imple- 

 ments are used. The greatest depth to which any soil 

 may be cultivated must be determined by the individual 

 farmer. There has been considerable opposition to deep 

 cultivation on the ground that it tends to destroy the 

 roots which feed in the upper layers of the soil. Some 

 plants are naturally more shallow-rooted than are others, 

 but an important thing in all arid agriculture is to com- 

 pel plant-roots to go deeply into the soil. Shallow-rooted 

 plants, under conditions of irrigation, usually indicate 

 that the farmer has used water unwisely by irrigating 

 too frequently or too heavily. Proper irrigation, moderate 

 in quantity and at proper intervals, causes practically 

 all the ordinary cultivated plants to strike their roots 

 deeply into the soil so deeply that no damage results 

 from the deep cultivation indicated by the experiments 

 here recorded. In many sections of the West, notably 

 in the orange districts of southern California, where the 

 rainfall is light and irrigation water scarce, deep culti- 

 vation has become a general practice in spite of the 

 general belief that citrous trees are shallow-rooted. 

 Before a rational irrigation practice is firmly established, 

 farmers must become convinced that there is no harm 

 whatever in cultivating deeply and as soon as possible 

 after each irrigation. 



40. Frequency of cultivation. Few experiments have 

 been conducted on this subject, but the principles already 

 laid down give a fairly clear indication of the cultivations 

 a field should receive throughout the season. Even after 

 a thorough cultivation, most soils gradually settle into a 

 more compact mass. In some soils this settling is so great 



