32 THE POTATO 



head, and a gradient of 0.1 foot in 100 feet. On 

 a marsh exactly level and with no part more than 

 half a mile from an outlet ditch, this means that 

 the 3 feet of depth at the head, added to the 2.64 

 feet of fall in a half mile requires a depth a little 

 more than 5J feet deep at the outlet. With an 

 allowance of 2J feet for the depth of the water in 

 the outlet ditch, it is evident that, under these 

 conditions, it should be dug 8 feet deep. Where 

 there is a surface slope toward the ditch, its depth 

 may be decreased by an amount equal to the fall 

 causing the slope. Following this rule, the depth 

 may, in rare cases, be reduced to 4 feet. Tile out- 

 lets may be submerged for a short time during 

 flood flow without serious results. 



"It is impossible to drain too deep for the 

 majority of farm crops. Our upland soils remain 

 moist where the water table is 100 feet or 

 more below the surface. It is true that a drained 

 peat unless compacted with a heavy roller will 

 dry out almost completely to a depth of from 3 to 

 6 inches. However, below that depth, it is un- 

 usual if the peat does not remain moist regardless 

 of the depth of the water table. 



"When plants '.dry up' in a peat soil it is an 

 indication that at some time the water table has 

 been so near the surface that only a shallow root 

 system was developed. With deep drainage from 

 the beginning, conditions favor the development 

 of a root system deep enough to reach through the 

 dry layer at the surface into the moist soil below. 

 This is the moisture that must be relied upon dur- 

 ing a drought. It is best to prepare for a drought 

 by deep drainage during the wet season of the 

 year. 



*'TilQ laid deep §eem to begin their increased 



