236 SOILS. 



should be widely used in irrigation countries to prevent the 

 injuries otherwise but too likely to arise from over-irrigation 

 (see chap. 12, p. 231). 



Winter Irrigation. In many regions where irrigation is 

 desirable but not absolutely necessary in ordinary seasons, or 

 where irrigation water is scarce in summer, much advantage 

 is gained by insuring thorough saturation of the land during 

 the latter part of winter, especially when spring or summer 

 crops are to be sown. The not inconsiderable time required 

 for \vater to reach its permanent level or the country drainage 

 in most soils, often insures the retention of a certain surplus 

 over what the soil can permanently hold, within the period 

 when it can be utilized by growing crops ; whose roots more- 

 over are more likely to penetrate deeply in land where there 

 is a steady increase of moisture as they descend, than when 

 the contrary condition is encountered. The use of winter 

 flood-waters to saturate the land is therefore in many cases the 

 saving clause for a dry season. 



METHODS OF IRRIGATION. 1 



The manner in which irrigation water is supplied to land 

 and especially to growing crops exerts such a potent influence 

 not only upon the welfare of the plants but also upon the condi- 

 tion of the land, that a brief discussion of this topic seems 

 necessary. 



The following methods are in use to a greater or less ex- 

 tent : 



1. Surface sprinkling. 



2. Flooding. 



A. By lateral overflow from furrows or ditches. 



B. By the " check " system. 



3. Furrow irrigation. 



4. Lateral seepage from ditches. 



5. Basin irrigation. 



6. Irrigation from underground pipes. 



1 Only a general outline of the principles of this subject is given in this volume; 

 special works must be consulted for working details. Among these the volume by 

 King on " Irrigation ami Drainage" gives probably the most comprehensive 

 presentation of the subject for both humid and arid climates. Also bulletins of 

 the U. S. Dep't of Agriculture. 



