92 Irrigation and Drainage 



sary that even frequent showers shall be supplemented 

 in order that the best results may be attained. 



In the second place, lands may be irrigated in any 

 climate, when it is desired to carry to the land ferti- 

 lizing matter which the irrigation waters may hold in 

 solution or in suspension. The extreme cases of this 

 practice are where cultivators take advantage of the 

 large amounts of plant -food which are borne along 

 in the waters of streams into which the sewage of 

 great cities, like Paris or Edinburgh, are discharged. 

 Such waters are extremely fertile, even when much 

 diluted. In emphasis of this fact, Fig. 19 shows a 

 field of heavy grass growing on the Craigentinny 

 meadows of Edinburgh. This ground yields from three 

 to five such crops each year, and has done so for 

 nearly a century, with no other fertilization than that 

 which comes to it through the winter and summer 

 application of diluted sewage water. Hence we need 

 not be surprised that such lands have rented as high 

 as 18 to 22 pounds sterling for the season per acre, 

 when the rentals are sold at auction to the highest 

 bidder. 



But ordinary river waters are widely used in vari- 

 ous countries, chiefly for the fertilization of water 

 meadows. The amount of water applied in a year 

 is in some sections very great, reaching, in the Vosges, 

 in France, over 300 feet in depth per year. It is 

 during the colder portions of the 3 r ear, when the grass 

 is not growing, that the larger part of the water is 

 applied, depending upon the absorptive and retentive 

 power of the soil to abstract from the water, as it 



