l8o JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



intermediate products which, as we shall see later on, might be 

 harmful both to bacteria and to plants. 



The story of the nitrifying organisms is an old one, but it bears 

 retelling. Only two organisms are known that can change ammonia 

 to nitrite, and only one that can change nitrite to nitrate. All three 

 are extremely small, and they are unique in that they build up their 

 substance out of carbon dioxide, obtaining the requisite energy from 

 the oxidation of the ammonia, and not from sunlight, as plants do. 

 They do not require organic matter either for food or for energy supply 

 — again a distinction from other micro-organisms ; indeed many organic 

 compounds are harmful to them. This property is so marked in 

 culture solutions that all organic matter was long supposed to be 

 harmful, but this is now known to be incorrect. Nitrification will take 

 place in presence of organic matter ; it is known to go on during 

 sewage purification, and it takes place regularly on the outside of a 

 dungheap. But there are two conditions which are highly detri- 

 mental to the nitrifying organisms, viz. acidity and lack of air. Pro- 

 vided these are avoided, the organisms will tolerate soil organic 

 matter. 



Running alongside of this decomposition is another. The amount 

 of nitrate formed is never as great as one expects from the nitrogen in 

 the protein, and the deficit is attributed to a loss of gaseous nitrogen. 

 We have, therefore, two possibilities : the protein may change to 

 nitrate or it may change to nitrogen. 



Now the evolution of gaseous nitrogen is of no value whatsoever 

 to the farmer or the gardener ; on the contrary, it represents a dead loss, 

 because the nitrogen is only dissipated. It is difficult to exaggerate 

 the seriousness of this loss to the intense cultivator. One of our plots 

 annually receives the liberal but by no means excessive dressing of 

 fourteen tons of dung to the acre, containing 200 lb. of nitrogen. Of this 

 about 50 lb. is recovered in the crop, and about 25 lb. remains in the 

 soil ; some also gets away in the drainage water. But about one half 

 of the nitrogen cannot be accounted for, and presumably it goes off 

 as gas at any rate the cultivator gets no benefit from it. 



It is impossible to form a precise estimate of the losses of nitrogen 

 in a market garden, but the conditions all favour high losses ; still 

 more do they do so in glasshouses where crops like cucumbers are 

 being grown. 



The market gardener is compelled to manure heavily in order 

 to secure heavy crops, and his loss of nitrogen simply represents the 

 extra price that always has to be paid whenever production is forced 

 beyond a certain level. But just as the engineer has learnt how to 

 increase the efficiency of an engine, so the cultivator has to learn how 

 to increase the efficiency of his production processes. This cannot 

 be accomplished until the nature of the soil-changes is better under- 

 stood and the cause of the loss of nitrogen has been revealed. The 

 action in the soil is too slow to allow of easy investigation ; it is marked 

 enough to cause serious loss over an acre in a year, but not in the 



