232 MANURES FOR TREES 



constituents of the plants he desires to grow, and 

 the composition of the soil. He is then in a 

 position to manure correctly and with economy. 



Phosphates. — In addition to bones and 

 guanos, there are coprolites and mineral manures. 

 The phosphates in these manures are generally in 

 an insoluble form, and — like bones — they require 

 time to decompose. They cannot be utilised at 

 once by the roots of trees and shrubs. If mineral 

 phosphates are used in special manures they must 

 be employed in large quantities. 



' Thomas Phosphate, or basic slag, is a phos- 

 phatic manure produced as a bye-product in the 

 manufacture of steel by the basic process. Thomas 

 phosphate contains in 100 parts : — 



"Thomas slag is a very heavy, dark-coloured 

 powder, containing much oxide of iron, but that is 

 not at aU injurious to crops " (Munro). 



