loo NITROGENOUS MANURES [chap. 



unit of nitrogen in dried blood is always expensive, 

 because of the limited supply of this material and the 

 special value to manure manufacturers it possesses for 

 compounding purposes ; in rape cake, nitrogen is also 

 greatly above the average price, because of the compara- 

 tively short supply of this manure. Again, in Peruvian 

 guano the unit of nitrogen always costs more than in 

 the average run of manures, whereas in fish and meat 

 guanos it ranges at almost the same price as in sulphate 

 of ammonia. Finally, in all the shoddies and waste 

 materials of that nature the price of the unit of nitrogen 

 is extremely variable, a large proportion being made up 

 by the cost of carriage of so bulky a material, but, as a 

 rule, it will not be more than one-half of the price asked 

 for nitrogen in its more available forms. At the time of 

 writing, the unit of nitrogen in Peruvian guanos costs 

 about 1 8s. and rather more in dried blood and rape dust, 

 in fish guano about 17s., in nitrate of soda about i6s., 

 in meat guano about 14s., and in sulphate of ammonia 

 about 13s., while shoddies can be obtained in which it 

 costs as little as 6s. 



Putting aside shoddy, it is thus seen that the 

 farmer is prepared to pay more for nitrogen in any 

 form of organic combination than in its inorganic salts, 

 though all the experimental evidence goes to show that 

 the latter give the larger and speedier returns in the 

 crop. 



What, then, is the origin of this strong prejudice 

 of the farmer in favour of an organic source of nitrogen, 

 the prejudice which is further seen in the common 

 description of nitrate of soda and sulphate of ammonia 

 as stimulants or even " scourges " of the soil, rather than 

 plant foods? Of course, no purely nitrogenous sub- 

 stance is a complete manure ; cropping with one alone 

 must eventually exhaust the land of phosphoric acid or 



