CHAPTER XIV 



SEWAGE-IRRIGA TION 



The application of sewage to the land may be 

 prompted by economic or sanitary considerations, or 

 by both. In countries of slight rainfall, sewage possesses 

 a certain value entirely apart from the plant-food it 

 may contain, since it may be advantageously employed 

 for the sake of its water alone. The arid and semi-arid 

 lands of the West yield profitable returns from sewage- 

 irrigation for this, if for no other reason. Even in regions 

 of more abundant rainfall, the application of sewage 

 to light, sandy soils with small capacity for retaining 

 water, is very beneficial. Soils of this type need large 

 and frequent applications of water for the production 

 of maximum crops, even when plant-food is abundant. 

 On the sandy soils of southern New Jersey, irrigation 

 has been found to increase the yields ' notwithstanding 

 the forty-five to fifty inches of annual rainfall. 



Economic value of sewage-irrigation. — Sewage pos- 

 sesses a still further interest, economically, on account 

 of the plant-food constituents contained in it. The 

 nitrogen, phosphoric acid, potash, lime and other plant- 

 food removed by the crops from the soil are carried 

 in part to the city to be discharged ultimately into the 

 sewers and thence to the sea. The land is thus gradually 



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