TILLAGE TO SAVE MOISTURE 69 



troublesome and expensive and otherwise objectionable, although 

 it has an acknowledged place in garden practice, as will be shown 

 later. 



The Earth Mulch. California practice has made the widest 

 application of the truth that a finely pulverized surface layer of 

 sufficient depth is an effective mulch. Pulverizing the soil widens 

 the distance between its particles and consequently destroys its 

 capillarity until by the action of moisture, either in the form of 

 liquid or vapor, it becomes again compacted to a degree which re- 

 stores its power to transmit moisture. The cultivator has it, then, 

 within his power to spread a mulch and check evaporation simply 

 by fine and frequent pulverization of the surface layer by cultivation. 

 It is this ability which enables the California horticulturist to trans- 

 form the lower layers of his soil into a reservoir, and to profit by 

 the natural tendency of the moisture to rise in the compact soil until 

 it reaches the point where the pulverized layer checks its advance. 

 This practice makes possible an achievement which seems almost 

 incredible to workers in humid climates, viz.: the growing of a 

 succulent crop from seeding to harvest without the use of a drop 

 of water either by rain or irrigation, and it is this practice, coupled 

 with the deeper rooting habit of plants which is induced by it, which 

 enables our trees and field crops to grow thriftily and produce 

 heavily during months of drought, while a few weeks of drought 

 may bring distress to plants in humid climates. 



But the pulverized surface layer must do more than arrest the 

 capillary rise of moisture before it reaches the surface : it must check 

 it at a point out of reach of the free entrance of air through the 

 loose layer, consequently the degree of pulverization and the depth 

 of the loose layer are factors to be carefully observed. It is not 

 enough to grind an inch or two of the surface to powder. The free 

 movement of air through this shallow layer, at least in our summer 

 air with its exceptional thirst, will proceed with evaporation from 

 the too thinly covered compact portion and the loss of moisture will 

 be onlv a little less rapid and complete than if the surface had not 

 been disturbed at all. The same thing will happen if the surface 

 layer be only coarsely broken to a still greater depth : the passage of 

 air through the clods will be free enough to draw off the moisture 

 and the soil will dry out to a degree which will bring distress to 

 plants which good cultivation would have maintained in vigorous 

 growth. It is plain, then, that the earth mulch must be fine enough 

 and deep enough to serve its intended purpose and for this no arbi- 

 trary rule can be laid down except that the coarser the soil by nature, 

 or the coarser the particles by cultivation, the deeper the mulch 

 must be. The practical test is easy ; if the pulverized layer becomes 

 dry and if on brushing it aside with the foot, the earth below is 

 hard and more or less dry also, the mulch is not effective and its 

 character must be improved. 



