WHAT IS MEANT BY DRY FARMING 19 



recently plowed. The plowing causes the particles to 

 lie loosely. The dry air enters readily and passes between 

 them in its onward movement, and in its exit carries 

 away more or less of the moisture. The more prompt 

 and complete the compression, the less is the loss of 

 moisture. The object of the soil mulch is to prevent 

 the escape of moisture that moves upward in the soil, 

 on the principle of capillarity. The dust mulch may be 

 maintained most readily in land that is summer-fallowed, 

 because of the unlimited opportunity given for renewing 

 it. It may also be readily maintained in areas that are 

 planted to crops which call for cultivation while they 

 are being grown. It may be maintained in cereals in 

 many instances until these become large enough to form 

 for themselves what may be termed a shade mulch. Most 

 difficult of all is it to maintain a dust mulch on grasses. 

 In many instances it may be unwise to attempt this. 

 For the further discussion of the retention of soil 

 moisture, see pp. 165-172. 



Organic matter in the soil increases its power to 

 hold moisture and in a marked degree. In the process of 

 decay it absorbs moisture as a sponge absorbs water, 

 thus influencing its passage downward or upward. It 

 tends to fill the soil spaces in leachy soils so that water 

 cannot percolate down through them so readily. It 

 has been said that in semi-arid areas a soil well supplied 

 with organic matter will grow an equal crop on half the 

 amount of the precipitation that will be called for by a 

 soil similar in its physical constituents but destitute of 

 organic matter. Organic matter also influences favor- 

 ably the physical condition of the soil and furnishes food 

 in a readily available condition for the feeding of crops. 

 See also pp. 414-423. 



Contrasted with farming in humid areas. Dry farm- 

 ing differs from other farming in at least the following 

 senses: (1) It is confessedly more difficult. (2) It calls 



