86 DRY LAND FARMING 



Evaporation at the surface means the loss of mois- 

 ture from the soil as it climbs up through the pore spaces 

 in the same to the surface, where it becomes vaporized 

 as it becomes incorporated with the air. To prevent 

 loss from this source is of the utmost importance to 

 the farmer in dry areas, hence the extent to which this 

 question is dwelt upon below. Under the most favor- 

 able conditions the amount of moisture in the soil is 

 less than could be utilized to the best advantage. If 

 this should be lost or any large portion of it, the farmer 

 is undone for that season. In dry farming the handling 

 of the soil in a way that will cause the precipitation fall- 

 ing upon the soil to enter the same to the greatest 

 extent possible is fundamental, and of no less importance 

 are measures that will tend to prevent the escape of mois- 

 ture to the greatest extent possible until it has been 

 utilized in growing plants. 



Loss of moisture by transpiration means the passing 

 of moisture into the air through the leaves of the plant 

 which has been taken from the soil by the roots. This 

 process is continuous while growth lasts. It is a loss 

 that cannot be lessened very much by those who till 

 the soil. But the harm that may follow to succeeding 

 crops may be minimized and in many instances entirely 

 prevented by wisely regulating the rotation followed. 



Loss of moisture by leaching is of course the loss of 

 water that has passed down through the soil into the 

 subsoil, whence it moves on and out as drainage water 

 into streams. It seldom occurs in dry areas, because 

 of the small quantity that enters the soil. In humid 

 areas the water that passes down through the soil carries 

 with it in solution much plant food that has been taken 

 out of the soil. The richer the soil and the more abun- 

 dant the precipitation the greater is the loss from this 

 source. This explains, in part at least, why soils in areas 

 of much rainfall frequently call for much fertilization, 



