LOW GRADK NITROGKNOUS MATERIALS, ETC. 63 



render the nitrogen available. When treated by either of the 

 above methods, it is known as dissolved wool, shoddy, etc., and 

 is of course more valuable than the raw products from which 

 it is made. 



Garbage Tankage. — Many of the large cities have plants where 

 the garbage is accumulated. It is dried, or charred, or steamed, 

 or extracted and the treated product is sold as garbage tankage. 

 This material contains about 2 per cent, of nitrogen which is in 

 a form that is slowly assimilated by plants. It is not a valuable 

 fertilizer.* 



Dried peat, sometimes called dried muck, is used principally by 

 the 'manufacturers because of its excellent drying properties. 

 The use of it enables the manufacturer to put out a fertilizer 

 in a fine mechanical condition which may be distributed evenly 

 on the soil. This material varies in composition, depending on 

 the amount of vegetable and mineral matter present, but may be 

 considered as averaging 1.5 to 2 per cent, of nitrogen. 



Availability of Nitrogenous Fertilizer Materials. — The only cor- 

 rect way to determine the value of any nitrogenous substance is 

 by running experiments with growing plants. The high grade 

 products as nitrate of soda, sulphate of ammonia, dried blood, 

 cotton-seed meal, linseed meal, castor pomace, dry ground fish, 

 tankage, ground bone, steamed horn and hoof meal, etc., have 

 been tested by field experiments to determine their crop produc- 

 ing power. Laboratory methods have been introduced to corre- 

 spond as near as possible with the field results. 



The availability of nitrate of soda is always taken as 100 and 

 the availability of the other materials is based on the results 

 secured when compared to nitrate of soda. Should nitrate of 

 soda give an increased yield of 500 pounds per acre for a crop, 

 the yield of a nitrogenous fertilizer of 75 per cent, availability 

 would give an increase of 375 pounds, etc. 



Not Always Possible to Run Field Experiments. — To conduct 

 field experiments is often impossible, because of the great expense, 

 the long time required, the difference in soils, the variation in 

 seasons, the ability of the various crops for securing plant food, 

 the association with other fertilizing materials containing phos- 



