648 SOILS: PROPJSBTIES AND MANAQBMBNT 



and the drain gradually increases in eflSciency. In heavy 

 soil and in soils having hardpan properties, several seasons 

 may be required for this change in the soil to spread 

 three or four rods from the drains. The problem is to 

 remove the excess water from the soil at the maximum 

 distance from the drains in time to avoid serious injury 

 to the crop. 



550. Constructioix of drainage trenches for tile. — 

 Trenches should be as small as possible and yet permit 

 the ready introduction of the tile. Unless the tiles to be 

 used are of the larger sizes, the ditch should be made 

 from twelve to fourteen inches wid^, with vertical sides. 

 Where leveling instruments are employed, the course 

 of the ditch is staked out and the grade cord is stretched 

 a definite distance above the proposed grade line of the 

 ditch, to guide the workmen. In hand digging, the earth 

 is thrown out with a narrow-pointed spade, the loose earth 



Pia. 66 — Tools for ditching (l) and (2) , ditching spades for remov- 

 ing the major part of the earth from the ditch , (3), grading scoop 

 used to finish the bottom of the ditch and the grade , (4) , skeleton 

 spade adapted for use m very plastic soil , (5) , shovel for removing 

 loose earth, (6), hook used to place tiJe m deep, narrow trenches, 

 (7) , pick for loosening stone and hard earth 



