FERTILIZERS 



141 



Fertilizing by Irrigation. To show the fertilizing value of 

 irrigation waters, some analyses are given below. 



COMPOSITION OF IRRIGATION WATER. 



Results expressed in parts per 1,000,000 



The waters of the Nile seeni to have the largest amount of 

 nitrogen, 1.7 per cent, all the others having merely a trace. 

 Some 24 acre-inches of Rio Grande water add to the soil about 

 1,075 pounds of potash, 116 pounds of phosphoric acid, and 

 107 pounds of nitrogen. The same amount of Delaware river 

 water contains 741.08 pounds of materials, while the Mississippi, 

 St. Lawrence, Amazon and La Plata rivers average 655.6 pounds 

 of solid matter for every 24 acre-inches. As a rule sewage 

 waters from the cities have the highest value for irrigation, 

 and muddy river waters stand next. Waters containing sul- 

 phate of iron are positively injurious when applied to land. 

 They usually issue from peaty or boggy swamps. While the 

 fertilizing value of sewage waters is unquestioned, and while 

 their use has been almost universally favored, objections have 

 been made to them on other grounds. To say the least, they 

 undoubtedly contain a hidden danger, and if used at all, it 

 should be with the greatest of care. It has been claimed that 

 "the use of sewage for fertilizing purposes is not to be com- 

 mended because of the danger of contaminating the soil with 



1 Kept. Mont. Exp. Sta., 1902, p. 62. 



a Exp. Sta. Record, V. 14, No. 11, p. 1057. 



