194 SOILS AND FERTILIZERS 



261. Seaweeds. Seaweeds are rich in potash and 

 near the sea coast are extensively used for fertilizer. 



Composition of 



mixed seaweeds. 



Per cent. 



Water 81.50 



Nitrogen o. 73 



Potash i .50 



Phosphoric acid o. 18 



262. Strand Plant Ash. Weeds and plants pro- 

 duced on waste land along the sea are in many Euro- 

 pean countries burned and the ashes used as fertilizer 

 on other lands. By this means waste land is made to 

 produce fertilizer for fields which are tillable. The 

 amount of fertility removed in weeds is usually greater 

 than that in agricultural plants, because weeds have 

 greater power of obtaining food from the soil. When 

 wheat or other grain is raised, and a small crop of 

 grain and a large crop of weeds are the result, there 

 is more fertility removed from the soil than if a heavy 

 stand of grain had been obtained. The ashes of strand 

 plants and weeds are extremely variable in composi- 

 tion. 



263. Wool Washings and Waste The washings 

 from wool contain sufficient potash to make them 

 valuable as fertilizer. In wool there is a high 

 per cent, of potash, which is soluble, and readily re- 

 moved in the washings. Wool waste may contain 

 from i to 5 per cent, of potash and from 4 to 7 per 

 cent, of nitrogen in somewhat inert forms. 



264. Street Sweepings. The horse manure and 

 debris collected from paved streets in cities and known 



