66 FERTILISERS CONTAINING NITROGEN [chap. 



a better return than an equivalent amount of nitrogen 

 in ammonium salts, although no other disturbing 

 factors, such as lack of potash or lime, intervene in the 

 cases quoted ; with barley, however, the yield is sensibly 

 equal from the two manures. At the time of harvest, 

 the crop grown with ammonium salts is always a little 

 the riper ; in the case of barley, this is of distinct value, 

 for it results in a more uniform product of higher quality. 

 Taking an average of fourteen years' valuations of the 

 barleys grown on the Rothamsted plots, the corn grown 

 with minerals and ammonium salts was valued at 104-3, 

 while the produce from minerals and nitrate of soda was 

 set at 100-3, ^^id that from the plot receiving farmyard 

 manure at 96-4 only, 100 being the average price of 

 barley for the year. These figures are calculated from 

 the cash valuations put on the various barleys every 

 year. With the mangolds again, it is seen that the 

 plants manured with nitrate continue to grow long 

 after those manured with ammonium salts have so 

 completed their season's growth that the leaves are 

 beginning to turn yellow and flaccid. All these 

 differences are explained by the deeper rooting habit 

 induced by the nitrate ; the plant is less affected by 

 the drought and the changes of temperature incident 

 to autumn, growth is more prolonged, with the cor- 

 ollary of a larger yield but a later and less uniform 

 maturity. 



One other factor may also contribute to the general 

 superiority of nitrate of soda. It must not be forgotten 

 that when a nitrogenous manure reaches the soil there 

 will be competition for it between the plant's roots and 

 the mass of living organisms present in the soil, nearly 

 all of which required combined nitrogen for their own 

 development. Some of these organisms, like the 

 nitrification bacteria, are wholly useful. Others cause 



