234 



SOIL PHYSICS AND MANAGEMENT 



and conditions. The soil mulch consists of a dry layer of soil, 

 either loose or compact. The loose mulch is far more effective and 

 common than the compact (Fig. 102). This latter results only 

 after much moisture has been lost from the soil, and should not be 

 depended upon. 



Some soils are self mulching to a certain extent. Sands, peats 

 and highly granular soils are of this character. The best way of 

 producing a soil mulch is by tillage, the kind of implement depend- 

 ing upon the soil, its tilth and moisture content, and the kind and 

 condition of the crop. 



Fineness of the Mulch. Mulches may be made too fine to he 

 of greatest value under all conditions. If fine- or medium-grained 



' 



FIG. 102. A good method of conserving moisture. 



soils contain little organic matter, cultivation tends to produce a 

 mulch of individual particles or a dust mulch, which, while it serves 

 very well for preventing evaporation, yet serves equally well for 

 preventing absorption of rainfall. Hence the first dash of a heavy 

 shower causes these particles to run together and produce an almost 

 impervious stratum. If the mulch is not so fine or is somewhat 

 cloddy or granular this running together does not take place so 

 readily and a much larger proportion of the rainfall will be ab- 

 sorbed. This in arid regions becomes a very serious problem where 

 it is desirable that all of the rainfall should be absorbed. Hence 

 a mulch should not be made with an implement that reduces the 

 soil to dust. 



