IRRIGATION 



265 



more than is economical. In the table the additional amounts of 

 water applied gave an increase in the total dry matter produced, 

 yet the increase of dry matter per acre-inch of water decreased. 

 The increase obtained was not always profitable. It will be noted 

 that the yield of wheat is 37.8 bushels per acre where five inches 

 of water were applied, while 7.5 inches gave a yield of 41.5 bushels, 

 or an increase of 1.5 bushels per acre-inch. When 2.5 inches more 

 were added the increase was 0.8 bushel per acre-inch, and when five 

 inches more were applied the increase was 0.4 bushel per acre-inch. 

 The next ten inches gave less than one-tenth of a bushel increase 

 per acre-inch. It is very evident that the point of profitable appli- 

 cation of water has been passed. 



The Producing Power of 30 Acre-Inches When Applied to Different Areas 



of Land 4 



30 Acre-inches spread over 



The one object to be kept in mind in irrigation is to grow the 

 maximum amount of dry matter with an acre-inch of water. Ex- 

 periments show that 10 to 20 inches is the most practicable amount 

 to apply. Larger amounts lower the quality of the grain and do not 

 give proportionate increases. 



The above table shows the value of small applications over more 

 extensive areas in comparison to the same application on smaller 

 areas. 



