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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



nitrogen compounds in abundance, together with phosphates, sulphates, 

 and other substances, and it offers the conditions necessary for the action 

 of denitrifying and nitrifying bacteria. 



The mineral theory with its chemical relationships and reactions in 

 the soil does not now offer the same satisfactory explanation of the 

 various processes of cultivation as it once did when it is compared with 

 what we now know of the action of soil bacteria. In fact actions that 

 were formerly attributed to chemical processes are now acknowledged to 

 be due to soil germs. For instance, the denitrification and liberation of 

 nitrogen in arable soils, now known to be due to a group of micro- 

 organisms, were for long regarded as purely chemical processes. Again, the 

 action we know under the term of nitrification was defined in 1846 as a 

 purely chemical process of oxidation, and was regarded as a purely chemical 

 process till 1888, when it was definitely determined that it was due to 

 the action of living organisms. There can .be little doubt that as our 

 knowledge of the soil and its bacterial content increases our dependence 

 on chemical theories will lessen. 



Even now questions on manuring — a process which is usually 

 regarded as an attempt to place plant-food material within the reach of 

 plants — can be answered differently from what they would have been a 

 few years ago. For example, horse dung is a " hot" manure because it 

 contains denitrifying organisms in enormous numbers. If it be brought, 

 especially when fresh, in contact with nitrates — nitrate of soda as a 

 dressing, for instance — a loss of nitrogen will result, or the nitrates 

 present in the soil will afford the special group of bacteria it contains an 

 undesirable field of activity. Again the " ripening " of stable or farmyard 

 manure is due to bacteria, and ifc is both an analytical and a synthetical 

 process. The fresh animal secretions consist of highly complex compounds 

 of nitrogen, and in the process of ripening through bacterial action they are 

 decomposed and reduced to nitrites, ammonia, and even free nitrogen. 

 Then a second process occurs, and, again through bacterial action, the results 

 of this decomposition are built up into nitrates. In fact, the profitable 

 cultivation of soil, according to the "new soil science" teaching, resolves 

 itself into the proper handling of bacteria. These organisms have stocked 

 the soil with plant-food material in the first place. They convert complex 

 organic bodies in the soil and added manures into simple bodies, some of 

 them becoming readily available as plant foods, while others are " lost " ; 

 and lastly, they may be made to reclaim the " lost " nitrogen. The natural 

 fertility, the acquired fertility, and the continued fertility of a soil arise from 

 bacterial action and depend on the cultivator's control of these organisms. 

 It is not only in respect to the preparation of plant-food material that 

 bacteria play a part, for even in the sprouting of seeds after they are sown 

 in the soil bacterial life has its influence. In fact the land-cultivator's life 

 from year's end to year's end is one that is in most intimate association 

 with bacteria. It has been well said that a " successful farmer's life 

 largely resolves itself into a skilful management of bacterial activity," 

 and that " the most successful farmer to-day, and we believe the most 

 successful farmer of the future, is the one who most intelligently and 

 skilfully manipulates these gigantic forces furnished to him by the growth 

 of his microscopical allies." 



