FERTILIZERS AND MANURES. 53 



of 'burning out' of the soil in dry seasons. Fresh manure 

 has a forcing effect, and is better suited to grasses and 

 forage plants than to plants grown for seeds, such as 

 cereals. Direct applications to root crops, such as sugar 

 beets, potatoes, or tobacco, often prove injurious. The 

 manure should be spread when carried to the field, and 

 not left in lumps to leach."* 



Commercial fertilizers are sold under two classes — 

 viz., "complete" and "partial," depending upon whether 

 the three necessary ingredients (phosphoric acid, potash 

 and nitrogen) are present or only one or two of them. 

 In determining which of these two classes of fertilizers 

 to use the gardener must be governed entirely by the 

 character of the plant and the condition of the soil. 



"Plants," says Liebig, "contain combustible and incom- 

 bustible ingredients. The latter, wmich compose the ash 

 left by all parts of plants on combustion, consist, in the 

 case of our cultivated plants, essentially of phosphoric 

 acid, potash, silicic and sulphuric acids, lime, iron, mag- 

 nesia, and chloride of sodium." It is now fully established 

 "that the constituents of the ash are elements of food, 

 and hence indispensable to the structure of the different 

 parts of the plant." 



The few ashes that remain after burning a plant are all 

 that it got necessarily from the soil. From eighty-eight 

 to ninety-nine per cent, of the weight of the plant has 

 escaped into the air, from which, and from water, the 

 plant has derived it immediately or remotely. The com- 

 position of their ashes varies in different parts of the same 

 plant and slightly in the same species when grown on 

 different soils; but they are always a valuable manure for 

 the species from which obtained, and, slowly dissolving 



*"Barnyard Manure," Farmer's Bulletin No. 21, U. S. Dept. Agri., p. 31. 



