218 NITROGENOUS FERTILIZERS 



and gelatine, then dried and ground. If little or no bone is 

 present the product is called meat tankage. If considerable 

 bone is present it is called bone tankage. Tankage is very 

 variable in composition, sometimes containing as much as 

 12 per cent, nitrogen in meat tankage, and up to 9 per 

 cent, nitrogen with 17 per cent, phosphoric acid in bone 

 tankage. 



Tankage is an excellent, rather slow acting fertilizer, its 

 value depending, especially in the case of bone tankage, on 

 fineness of grinding. The nitrogen is in the same form as in 

 dried meat and the effect on the soil is the same. 



164. Dried Fish, Fish Scrap. — The refuse material from 

 fish oil refineries, fish salting, or canning plants is dried 

 and ground, sometimes being treated with dilute sulphuric 

 acid to stop decomposition and partially dissolve the bones. 

 This fertilizer contains from 6 to 9 per cent, nitrogen and 

 5 to 9 per cent, phosphoric acid. Fish scrap is about as good 

 as the better grades of tankage, though slower acting than 

 dried blood. It contains the protein form of nitrogen. 



165. Cottonseed Meal. — The press cake which results from 

 the extraction of oil from cotton seed is used extensively 

 as a fertilizer. The decorticated meal made from seeds 

 which have had the husks removed before pressing, runs 

 about 6 per cent, nitrogen; the undecorticated meal carries 

 only 4 per cent, nitrogen. There are also small amounts 

 of phosphoric acid and potash. Since cottonseed meal is an 

 excellent cattle food, and since most of its fertilizing con- 

 stituents are recovered in the manure, it is much more 

 profitable to feed it first and use the manure as a fertilizer. 

 But it is, nevertheless, used to a very large extent directly 

 as a fertilizer, especially in the south. Moreover, its physical 

 condition is such that it improves the mechanical condition 

 of mixed fertilizers by absorbing moisture and preventing 

 caking. Its availability is about the same as dried blood 

 and the form of nitrogen is similar. 



166. Castor-Bean Pomace. — This is the ground press cake 

 from the manufacture of castor oil, and contains about 

 5 per cent, nitrogen with some phosphoric acid and potash. 

 It is a good fertilizer. 



