378 BOARD OF AGRICULTURE. [Pub. Doc. 



a more thorough and permanent work will be insured by 

 bedding and covering the entire tile with it. 



Under-drains should be deep enough to encourage the 

 fullest development of root growth, to avoid any disturbing 

 and integrating effects from freezing and to escape the danger 

 of being obstructed by roots entering at the joints. Lower- 

 ing the water table much below the greatest depth of root 

 action diminishes the moisture raised by capillarity, and is 

 therefore disadvantageous. Subject to these considerations 

 and to such variations as the necessities of the grade of the 

 drain and the inequalities of the surface of the ground may 

 involve, from three and one-half to four and one-half feet is 

 a fair average depth to adopt. Less may be used where a 

 low or deep out-fall cannot be had, as in the case of flat lands 

 situated at a slight elevation above an adjacent pond or 

 stream which fixes the level at which the main drain may 

 discharge. 



The distance between drains is governed chiefly by the 

 greatest depth, within the limits already stated, at which 

 they can be laid, and by the permeability of the soil and 

 subsoil to be drained thereby. In clayey soils, through 

 which water percolates but slowly and with the greatest diffi- 

 culty, the drains should be placed at a distance of about six 

 to seven feet for every foot of their depth ; while for loamy 

 soils, underlaid by sand, equally good drainage may be se- 

 cured if the drains are laid at nearly double that distance 

 apart, or ten to fifteen feet for each foot of depth, depending 

 upon the porosity of the underlying material. Thus in clay 

 or hard-pan drains three or four feet in depth should be laid 

 from twenty to thirty feet apart, and for soils underlaid by 

 sand the distance (for the same depth) may be forty or fifty 

 and sometimes sixty feet, while in material of intermediate 

 character or porosity a distance of thirty to forty feet would 

 be suitable. 



Without discussing the various considerations affecting 

 the sizes of tile to be used, it may be said that one thousand 

 feet laid forty-five feet apart will drain an acre of land un- 

 derlaid by a permeable soil, and that the maximum amount 

 of ground water collected and discharged thereby would 



