Kinds of Crops Under Sewage 131 



is prepared carefully by thorough underdrainage, and 

 the influences injurious to intense bacterial activity 

 are eliminated as far as possible. The treatment of 

 sewage by intermittent irrigation is, therefore, much 

 akin to its treatment in bacterial filters. 



Satisfactory results from sewage-irrigation are se- 

 cured when broad and intermittent irrigation are com- 

 bined. A portion of the land, properly prepared and 

 underdrained, is employed for intermittent irrigation 

 when the sewage cannot be used to advantage on the 

 growing crops. In this manner, the land is not made to 

 receive more sewage than it can readily purify. More- 

 over, the entire process becomes, in a way, intermittent, 

 since the application of sewage is not too frequent, nor 

 too severe to permit adequate aeration. 



The crops grown on sewage-farms. — These must be 

 capable of transpiring large quantities of water, and 

 must otherwise be adapted to the soil conditions. Italian 

 rye grass has been grown extensively on the sewage- 

 farms in England and Scotland. It grows very rapidly, 

 crowds out weeds, and yields several heavy cuttings 

 in one season. It requires reseeding every three years, 

 although usually it is succeeded at the end of that time 

 by other crops, like mangolds or cabbages. On some of 

 the irrigated meadows the rye grass has been replaced 

 by a mixture of native grasses which likewise produce 

 heavy yields of dry matter. Alfalfa has also been grown 

 successfully on sewage-irrigated lands near Paris and in 

 our western states. Like the Italian rye grass, it trans- 

 pires enormous quantities of water. On the whole, how- 

 ever, leguminous crops are not adapted for sewage-farms. 



