Sewage Waters for Irrigation 253 



Using the figures of T. M. Read* regarding the 

 amount of materials which the great rivers of the 

 world bear in solution to the sea, it appears that the 

 Mississippi and St. Lawrence rivers, in North America, 

 and the Amazon and La Plata, in South America, 

 carry an amount such that the average is 655.6 pounds 

 per each 24 acre-inches of water. 



Goss and Haret, from analyses of the water of the 

 Rio Grande at different periods from June 1 to Octo- 

 ber 31, compute that 24 acre-inches of the water 

 contained in sediment and in solution 1,075 pounds 

 of potash, 116 pounds of phosphoric acid, and 107 

 pounds of nitrogen. The water of this river contains 

 a sufficient amount of sediment so that 24 acre- inches 

 of it furnishes 81,309 pounds, or more than 4 tons 

 per acre. 



It is evident from these data that the ordinary 

 clear waters of rivers, lakes, springs and wells cannot 

 be expected to bear to the fields upon which they are 

 applied a sufficient amount of plant -food to meet the 

 needs of crops, unless the water is applied in much 

 larger volumes than is required to meet the demands 

 of soil moisture. 



SEWAGE WATERS FOB PURPOSES OF IRRIGATION 



It may be laid down as a general rule that the 

 water of highest value for the purposes of irrigation 

 is the sewage of large cities, unless it contains too 



*Am. Jour. Sci., vol. xxix , p. 290. 

 fNew Mexico Expt. Sta., Bull. 13. 



