THE DRAINAGE OF FARM SOILS 219 



40 to 70 feet on average loams with a rather open 

 subsoil, and 100 and even 200 feet on very open 

 soils. A safe distance for average loam soils in 

 the Eastern and Central States is 40 to 50 feet, if 

 the depth is not less than 3J feet; and 25 to 40 feet 

 on heavy clay soils. Many fields may be ex- 

 cellently drained with some lines of tile 40 feet and 

 some 100 feet apart, according to the nature of the 

 soil in different parts. 



DEPTH OF UNDER-DRAINS 



The deeper the drains are placed, within reason- 

 able limits, the better they work. But beyond a 

 certain depth the expense of moving soil increases 

 faster than the advantage gained in the way of 

 better drainage. In certain soils it may cost about 

 twice as much to dig a ditch four feet deep as it 

 does one three feet deep. For ordinary farm crops 

 the depth to which the ground water should be 

 lowered need not be over four feet, and frequently 

 less. If the land is too wet only in the early 

 part of the season, and it is desired merely to 

 lower the water-table sufficiently to dry out the 

 land quickly in early spring, drains placed two 

 and one-half or three feet deep will usually 

 answer the purpose. 



It may happen that the only available outlet is 

 so high that it is necessary to place the drains at less 

 depth than what is considered best, so as to secure 

 sufficient fall for the entire system. Again, if the 

 field has a sandy or gravelly subsoil some four or 

 five feet below the surface, it would be unwise 

 to place the drains so deep that the water-table 

 would be lowered into the sand or gravel, because 

 this coarse soil has poor capillary power and the soil 



