PART III 



FERTILISERS 

 CHAPTER VII 



THE NITROGENOUS FERTILISERS 



In attempting to satisfy the various fertility require- 

 ments discussed in the previous chapter it becomes 

 necessary to increase the amount of plant nutrients in 

 the soU and to this end various substances are added 

 which are known as fertilisers and manures. The dis- 

 tinction between the two terms is not very sharp, but 

 generally a fertiliser is a concentrated substance im- 

 ported on to the farm from a foreign country or a 

 factory, and therefore is frequently called an artificial 

 fertiliser, while a manure is a more bulky material either 

 produced on the farm or closely related to farm pro- 

 ducts. 



The substances thus added to the soil are compounds 

 of nitrogen, phosphorus and potassium: also organic 

 matter and lime or chalk. In order to study their effect 

 on the soil a series of pot experiments should be started : 

 10 inch flower pots are sufficiently good for ordinary 

 purposes but for finer work Doulton's glazed pots must 

 be used (Fig. 1). The soU has to be carefully mixed to 

 ensure uniformity and if it is heavy 10 to 20 per cent, 

 of sand must be added. The series should contain pots 



