DRY FARMING 175 



down weeds prevents plant-food from being di- 

 verted from the crop. This is beneficial, not to 

 dry lands only, but to all lands, though we have 

 to thank the dry farmers for directing attention 

 to the supreme importance of the hoe in success- 

 ful agriculture. Air promotes evaporation, and in 

 so far as the mulch extends moisture is probably 

 being continually lost. 



Dry farmers are on safer ground when they 

 insist on the fallow as a means for conserving 

 the moisture of the soil. Lawes and Gilbert 

 found that, for barley, 257 lb. of water were 

 transpired for every pound of dry matter pro- 

 duced ; Wollny gave 774 lb. Plants transpire 

 more water per pound of dry matter produced in 

 a poor soil than in a rich. This may be due to 

 the moisture absorbed being less concentrated in 

 soluble plant- food. Leather found that the pro- 

 portion of water transpired was less on manured 

 than unmanured soil. Manure can thus take the 

 place of water to some extent. A plant may be 

 regarded as a pump sucking up the moisture from 

 the region of the soil searched by its roots and 

 dissipating it into the atmosphere. It is easy to 

 understand that if we keep our land free from 

 plants for six months or a year we shall effect a 

 great economy in water and store up accumula- 

 tions of rainfall for a future crop. 



