MANAGEMENT OF MULCHES 205 



below. Since in humid regions drying is usually slow and 

 capillary movement strong, the process is hastened by 

 loosening the top soil by frequently stirring, in order 

 (1) to hasten the drying of that surface portion to the 

 point where capillarity is stopped, and (2) to reduce its 

 capillary conductivity, both of which hasten the forma- 

 tion of the mulch. It is for these reasons that a mulch 

 is generally a loose layer of soil. 



The management of the mulch is evident from the 

 principles involved. It must be kept dry in order to break 

 up capillarity. In humid regions, where frequent rains 

 occur, the mulch may be destroyed. After such a rain, 

 when the soil has reached the proper dryness, it should 

 be again stirred, to renew the mulch. On heavy clay 

 soil in fine tilth, a mulch may be destroyed by very 

 moist foggy weather, or by a number of days of very 

 humid atmosphere, which, by condensation of moisture 

 on the clay, hastens the reestablishment of capillarity 

 with the subsoil, by which moisture may be pumped 

 up and lost. This is to be overcome by occasional stir- 

 ring, as conditions may require. Another important 

 effect of the mulch on clay is to keep the shrinkage 

 cracks filled up, and thereby prevent the deep drying- 

 out of such soil. 



When perfectly dry, a coarse sand and a pulverized 

 clay are of almost the same practical efficiency. (See 

 page 190.) It is only when the structure becomes that 

 of coarse clods or stone that the efficiency is greatly 

 reduced. A cloddy surface soil is worse than a smooth 

 surface with no mulch, for the clods are free to evaporate 

 water, and offer small protection to the subsoil. On 



