204 SOILS 



current quickly undermines steep banks unless 

 the soil is very fibrous or clayey. It is usually 

 best to grass over open ditches ; some sort of herb- 

 age will soon cover the banks anyhow, but grass 

 roots are more valuable as soil binders. 



The distance apart of open ditches is governed 

 entirely by the nature of the land. In marsh land 

 the small laterals, which may be about three feet 

 deep and three feet wide on the bottom, are fre- 

 quently placed from 40 to 100 feet apart, and 

 empty into larger main ditches, which are five or 

 six feet deep and equally wide on the bottom. 

 In some cases it is better to dig larger ditches from 

 150 to 200 feet apart. 



PLOWING INTO LANDS 



This simple and very common device for surface 

 drainage has already been mentioned in Chapter V. 

 It is useful solely for removing the excess of free 

 water, especially that which stands upon the sur- 

 face. Plowing a field into lands makes, very 

 shallow open ditches. It is quite common to 

 leave dead-furrows about fifteen or twenty feet 

 apart, thus throwing the soil into slightly 

 raised beds or lands. The dead-furrows should 

 usually lead to open ditches on the side of the 

 field. This dries out the soil and warms it 

 earlier in spring. 



If the soil is liable to remain wet late into the 

 spring, and especially if it is a heavy clay, the dead- 

 furrows may be in the same place for several years, 

 thus deepening the hollows and elevating the lands. 

 On average soils, however, the dead-furrows should 

 be made in different places each year. According 

 to Roberts, lands five or six paces wide do not 



