CROP COMPOSITION 



219 



drying-out cannot be so complete. Stewart has shown 

 that this difference may have very noticeable financial 

 results when large shipments of grain are made from the 

 arid regions. 



129. Ash. The ash, or incombustible portion of 

 plants, represents, roughly, the food taken from the soil 

 by the plant. It is, therefore, important in considering 

 the maintenance of soil fertility. The effect of much or 

 little soil moisture upon the quantity of ash taken up 

 by the plant has been investigated by many students. In 

 general, the percentage of ash in the dry substance be- 

 comes larger as the quantity of irrigation water or the 

 soil moisture increases. The following table shows some 

 typical results under irrigated conditions : 



As the supply of water increases, there is usually a 

 very marked increase in the percentage of ash in the 

 leaves, a smaller increase in the stalks, and a yet smaller 

 increase in the underground parts of the plant. This 

 relative variation among the plant parts seems to be a 

 general rule, although observations are on record show- 

 ing a decrease in the percentage of ash hi the under- 

 ground parts as the irrigations are made larger. 



Tollens and others have shown that, in general, this 

 law of increase is true for each ash constituent as for the 

 total ash. Lime is taken up very abundantly by the plant 



