68 VEGETABLE FORCING 



commercial fertilizer. It contains about 15 per cent of 

 nitrogen. The salt dissolves quickly in the moisture of 

 the soil, when it immediately becomes available to plants. 

 This is usually the cheapest form of nitrogen. 



Sulphate of ammonia, which is formed from waste 

 materials produced in the manufacture of illuminating 

 gas, is used sometimes in the fertilizing of greenhouse 

 crops. It is more concentrated than nitrate of soda, since 

 it contains about 20 per cent of nitrogen. Lime should 

 be used in conjunction with large applications of 

 sulphate of ammonia in order to prevent unfavorable 

 chemical conditions in the soil. 



Of the organic fertilizers, dried blood is probably the 

 most popular. It consists of blood from the animals 

 slaughtered in the great packing houses, and is prepared 

 for market by evaporating, drying and grinding. The 

 best grades of dried blood contain from 12 to 15 per cent 

 of nitrogen. While dried blood is not nearly so available 

 as nitrate of soda, it decomposes very rapidly in the 

 warm, moist soils of the greenhouse, and when properly 

 applied produces most excellent results. 



Different grades of tankage are also available for 

 greenhouse crops. They vary greatly in the amount of 

 nitrogen which they contain, and also in the fineness of 

 the particles. Tankage consists of all sorts of miscel- 

 laneous refuse of packing houses. 



Other forms of nitrogenous fertilizers are used occa- 

 sionally in the greenhouse, but they are not important, 

 except the various forms of animal bone which contain 

 some nitrogen. These are especially popular among 

 florists. The bone preparations seldom contain more 

 than 4 or 5 per cent of nitrogen. The nitrogen in bone 

 meals becomes available very slowly, and this is the 

 most serious objection to their use for greenhouse crops. 

 On the other hand, large quantities of bone meal may be 

 used with perfect safety, and this knowledge adds greatly 



