224 IRRIGATION PRACTICE 



132. Carbohydrates. The substances included in this 

 group are used hi the animal body for the production of 

 heat and the formation of fat. The carbohydrates are 

 very important foods; but, since they are quite abun- 

 dant, they are of less value than the protein. The elements 

 constituting the carbohydrates are drawn from the water 

 of the soil and the carbon dioxide of the air, both of which 

 are more easily supplied than the ash or the nitrogen, 

 the essential element in protein. For agricultural pur- 

 poses it is necessary to consider under the head of carbo- 

 hydrates the sugars, starches, and the woody substances 

 or crude fiber. It has been well established that the per- 

 centage of total carbohydrates in a plant increases as the 

 quantity of irrigation water increases. That is, the per- 

 centage of the sum of all the carbohydrates varies in the 

 opposite direction from protein, as the quantity of irriga- 

 tion water is varied. 



133. Sugars. The sugars are many. The best known 

 is beet or cane sugar. As a general though not an invariable 

 rule, the percentage of sugar in a crop decreases as irriga- 

 tion water increases. In the following table are presented 

 a number of data secured by Jones and Palmer, in a study 

 of fruits grown in Idaho. In the one column is the com- 

 position of irrigated, in the other of non-irrigated fruits. 

 The locality in which these fruits grew receives a rather 

 large rainfall, and the conditions are not those prevailing 

 under true arid conditions. The non-irrigated crops may, 

 therefore, really be compared to those that have received a 

 small irrigation, and the irrigated crops to those that have 

 received a heavy irrigation: 



