Mineral Nutrients 



149 



sition and conversion into ammonia and nitrates that the 

 numerous important organic nitrogen fertilizers, such as 

 stable and green manures, dried blood, tankage, and the 

 like, are to any practical extent valuable for plants. De- 

 composition and nitrification processes, however, will be 

 discussed later. 



FIG. 46. Tobacco experiments : Plat 1, no fertilizer; Plat 2, acid phos- 

 phate. [Photograph from the Ohio Agl. Exp. Sta.] 



The soluble phosphates of the various bases are all imme- 

 diately available and may be used in water cultures ; but 

 phosphates are frequently applied to the soil in some 

 insoluble form, such as bone-meal or phosphatic rock, 

 which become gradually available by chemical changes in 



