48 AGRICULTURE ON THE PACIFIC SLOPE 



The action of the soil mulch may be understood by 

 what happens with a brick and sponge (figure 23), 

 Soak a brick in water until no more bubbles rise from 

 it, and then lay it on a dry sponge. Does the sponge 

 take any water out of the brick ? Now wet the sponge 



FIG. 23. Brick and sponge showing action of mulch. The sponge acts like 

 a mulch because it cannot take water from the brick. 



well and lay a dry brick on it and note how the brick 

 sucks up the water and leaves the sponge almost dry. 

 The loose soil mulch acts like the dry sponge ; the wet 

 brick like the moist soil below, from which the loose 

 mulch cannot draw the moisture to the surface. But 

 if, instead of the mulch, a hard crust, from the beat- 



