128 Fertilisers [pt. hi 



treated as follows: (1) unmanured; (2) and (3) 0-01 and 

 0-05 per cent, respectively of nitrate of soda; (4) 0-1 per 

 cent, superphosphate; (5) 0-1 per cent, sulphate of 

 potash; and three or four containing combinations of 

 these quantities; other pots should be supplied with 

 sulphate of ammonia in place of nitrate of soda, and 

 bone meal and basic slag in place of superphosphate. 

 If a glass house is available tomatoes are a good crop 

 for experiment; or at colder seasons mustard. For out- 

 door work rye, wheat or mustard do well. 



Two types of nitrogenous fertilisers are in common 

 use; nitrates which are ready and ammonium salts 

 which are almost ready for immediate use by the plant 

 and are therefore quick acting, and certain organic com- 

 pounds which have to undergo decomposition in the 

 soU. The first only are dealt with in this chapter. 



Nitrates 



Three nitrates are now available as fertilisers: the 

 nitrates of soda, of potash and of lime, and experiments 

 are being made with a fourth, nitrate of ammonia, but 

 of these the commonest is nitrate of soda (NaNOg). This 

 substance occurs in the rainless regions of Tarapaca and 

 Antofagasta in the north of Chile, where it forms de- 

 posits near the surface of the soil. The deposits occur 

 in detached areas stretching over a wide range and in 

 spite of the large annual consumption nearly 2,500,000 

 tons before the war there still seems a vast supply for 

 the future. It is not known how the deposits originated : 

 there is little doubt that they were once under water, 

 but there is nothing to sliow how so much nitrate came 

 to accumulate in one district: only traces occur in 



