190 NITROGEN AND ITS RELATION TO PLANTS 



Germany. Therefore valuable deposits of potash probably 

 exist there, and a thorough search is being made for them. The 

 Great Salt Lake of Utah is a relic of that western ocean, and 

 works have been established for extracting potash from its waters. 



Another source of potash is seaweed, especially the giant 

 kelp, which absorbs large quantities of potash from sea water. 

 The kelps are abundant, covering thousands of square miles 

 in the Pacific Ocean, from Mexico to the Arctic Ocean. Works 

 have been established for recovering potash from this source. 



Much potash is obtained from the mineral wastes of cement 

 making and other industries. 



Manure. The oldest and best known fertilizer is manure, 

 the excreta or waste matter of animals, and before the days of 

 commercial fertilizers the farmer depended solely upon stable or 

 barnyard manure for the improvement of his soil. Manure is 

 very valuable, since every ton of it contains about ten pounds of 

 nitrogen, eight pounds of potassium, two and one half pounds 

 of phosphorus, and small quantities of lime, magnesia, and other 

 substances needed by worn-out soil. Manure should not be 

 heaped in the barnyard because much of its valuable material 

 seeps into the soil and is lost. In addition, exposed manure 

 heaps ferment and become sour. A third argument against ex- 

 posed barnyard manure is that it serves as a breeding place for 

 flies and other obnoxious creatures. Modern stables in the city 

 and model farms in the country have brick manure pits in 

 which manure can be stored without loss from seepage or 

 from fermentation. 



Sewage, after chemical treatment, is likewise valuable as a 

 fertilizer and some large cities sell for fertilizer the more solid 

 portions of the sewage. It has been estimated that the sewage 

 of England alone would be worth eighty million dollars annually 

 as fertilizer. It is not improbable that in the future large cities 

 will use sewage as a source of income. 



