166 DRY LAND FARMING 



not sufficiently prevent the escape of soil moisture, hence 

 the combination of these forms the ideal dust mulch. Re- 

 peated harrowings in dry weather will probably result in 

 too much fining of the particles, whereas harrowing at the 

 opportune time after rains will result in that granular 

 condition of the soil which, in conjunction with the fine 

 soil particles, makes the ideal dust mulch. The name 

 "dust mulch" is something of a misnomer. The designa- 

 tion "soil mulch" is more appropriate. 



The mission of the dust or soil mulch is to prevent 

 the escape of moisture from the soil below the mulch 

 and also from the subsoil. When water climbs up from 

 below, on the principle of capillarity, it cannot pass 

 through a layer of dry earth. In the absence of such a 

 layer on the surface it climbs up and goes out into the 

 atmosphere insomuch that it is lost to the soil. When 

 rain falls so as to saturate the dust mulch it puts the 

 surface in that condition which facilitates the escape of 

 moisture, on the principle that capillary water can only 

 climb through a moist soil. When the dust mulch has 

 become thus saturated, on drying the soil contracts, with 

 the result that it becomes filled with numerous fissures. 

 Through these the moisture rapidly escapes into the air. 

 To check such loss of moisture it is necessary to harrow 

 the land as soon as dry enough to remove the encrusta- 

 tion, and to fill up the cracks. When the harrowing is 

 done at the right stage of dryness, it tends to insure that 

 granulated condition of the soil which is so favorable to 

 the maintenance of a dust mulch. Should such harrow- 

 ing be neglected or even too long deferred, the benefit 

 that would otherwise result from rain may be lost, as 

 when the .top soil is moistened it facilitates the climbing 

 of the moisture to the surface. 



The dust or soil mulch has an exceedingly important 

 place in all areas where the supply of moisture is less 

 than could be desired. The less the degree of the pre- 



