124 IRRIGATION PRACTICE 



gathered. It appears that crops which mature early use 

 water more rapidly than those which have a longer grow- 

 ing period. For example, under the conditions prevailing 

 in the irrigated sections of the United States, wheat and 

 oats use daily more water than corn, beets or potatoes, 

 although in the aggregate, wheat and oats use much less 

 water than do the longer-growing crops. Wheat, oats 

 and similar crops hasten on to maturity and, in so doing, 

 use water at a very rapid rate. Corn, potatoes and sugar 

 beets continue their steady growth throughout the season, 

 and the rate at which they use water is considerably 

 smaller. Lucern, which is cut from two to four or even 

 more times during the season, behaves pretty much as if 

 it were a series of quickly growing crops. 



The rate at which various crops use water may be 

 roughly estimated by the degree to which soils are dried 

 out during long periods without irrigation by the respec- 

 tive crops. Experiments show that, from this point of 

 view, lucern comes first, followed, in order, by wheat, 

 oats, corn, sugar beets and potatoes. This is practically 

 the order obtained in direct experimentation. More 

 information is needed regarding the relative powers of 

 different crops to abstract soil moisture. 



92. The seasons. The farmer may, in a measure, 

 control most of the factors already discussed, but Jie is 

 helpless when it comes to controlling the varying seasons. 

 No one factor is so powerful in influencing crop-growth 

 as are the seasons, and with this factor the farmer must 

 always reckon. The average temperature throughout 

 the season is of first importance in determining plant- 

 growth, and therefore, in a large measure, the rate at 

 which the plant uses water. With a high average tempera- 

 ture, plant-growth is rapid and the daily loss of soil 



