FIXING THE GRADE OF DRAINS. 9 1 



often penetrate them seeking moisture, they are quite 

 retentive, so that drainage-water passes through them 

 slowly. In such cases drains of less depth than 4 

 feet are of greater value for agricultural purposes. 

 When the statement is made that drains should never 

 be laid as shallow as 2 feet, it is confronted by the 

 fact that in many localities where the soil is exceed- 

 ingly retentive, and the subsoil more so, deep drains 

 have little immediate effect. Not that they are devoid 

 of value, or will not in time prove beneficial to the soil, 

 but their value will not be commensurate with their 

 cost. The more retentive the soil, the steeper will be 

 the line of saturation, and the less will be the breadth 

 of land which will be acted upon by each drain. 



It may be said that for farm lands, lateral drains 

 should be about 3 feet deep, unless the compact 

 and retentive soil indicates that less depth should be 

 used. When it is attempted to follow any general 

 depth the necessity of obtaining suitable grades for 

 the drains will often make some parts of the drain 

 deeper or shallower than desired. A nice and econom- 

 ical adjustment of the depths of the several drains of a 

 system can be learned only by practical work. A 

 practical knowledge of the field, coupled with the facts 

 on the field-book, form the key to the dormant re- 

 sources of the soil. 



Frequency of Drains, 



This is also a question upon which there is a wide 

 difference of opinion and a consequent difference of 

 practice. The science and art of land improvement 



