146 IRRIGATION PRACTICE 



soil during the season, there is a diminution instead of 

 an increase in the yield obtained. 



This question, however, remains: As the dry matter 

 increases with the increase in soil saturation, does the 

 water-cost of each pound of dry matter remain the same? 

 This matter has been investigated with considerable 

 care and with concordant results. Wilms found that 

 with a little water the transpiration ratio for potatoes 

 was 39; with more water, 50; and with much water, 61. 

 The Utah experiments showed invariably that with wheat, 

 sugar beets, corn, potatoes, alfalfa and all other crops 

 tested, as the quantity of water used was increased and 

 the yield thereby increased, the water-cost also became 

 larger. The general law is that, within the limits of 

 practical irrigation, the transpiration ratio increases as 

 the quantity of water added to the soil increases; that is, 

 that the water-cost of crops becomes larger as more water 

 is used in irrigation. Lyon and a number of his co-workers, 

 notably Morgan and Harris, as well as other students, 

 have confirmed this law, until it may be accepted as 

 being securely established. This is a matter of tremend- 

 ous importance. By using more water, the irrigation 

 farmer obtains a larger yield, but less for each unit of 

 water used. The question will always be, With how much 

 water will he get the largest possible returns from the 

 use of his land, water and labor? 



The only field experiments of any magnitude con- 

 ducted with a view of testing the effect of various quan- 

 tities of water on the production of dry matter and on 

 the water-cost of dry matter are those of the Utah Sta- 

 tion. Other experiments, not reduced to dry matter, will 

 be noted in later chapters. In the following table the 

 yields of dry matter in pounds to the acre ; with varying 



