The Science of the Soil 127 



University, states that in a black loam with a considerable amount of 

 humus there were 33,931,747 bacteria to 1 cub. cm., and as many as 

 53,596,060 in 1 cub. cm. of similar soil containing more humus. As there 

 are over 16 cub. cm. to 1 cub. in., and 1728 cub. in. to 1 cub. ft., one can 

 scarcely realize the teeming millions of bacteria there must be in a fertile 

 soil. Most cultivators will accept Professor Hilgard's figures to save the 

 trouble of counting them themselves. Speaking generally, the bacteria 

 may be classed into three groups: (1) The "decomposition" bacteria, that 

 attack and bring about the decay of manure and other organic matter; 

 (2) the "nitrifying" bacteria, consisting of two distinct organisms: the 

 one (a) Nitrosomonas, which converts ammonia into nitrous acid and 

 nitrite; the other (6) Nitrobacter, which changes nitrites into nitrates; 

 and (3) the "nitrogen-fixing" bacteria (Azotobacter), which absorb free 

 nitrogen from the air and fix it in the nodules of the roots of legu- 

 minous plants. 



Soil Inoculation. It has been known from the earliest times that 

 leguminous plants (Peas, Beans, Clovers, Vetches, &c.) had a beneficial 

 effect upon cultivated soils crops of a different nature grew better 

 after a leguminous crop. But it was not until 1886 that Hellriegel dis- 

 covered how the nodules on the roots of leguminous plants were really 

 storehouses of nitrogen-fixing bacteria, and further investigations are 

 being made by other scientists. 



Arising out of these discoveries Professor Bottomley conceived the idea 

 that, as the bacteria could be cultivated and isolated and kept for a long 

 time under certain conditions, it would be possible to " inoculate " a barren 

 soil a heap of slag or clinker even and bring it into a fertile condition 

 by the aid of these bacteria, and especially one called Bacillus radicicola. 

 In this way the "nitrogen famine", predicted by Sir William Crookes a 

 few years ago at a meeting of the British Association, was to be staved off. 



Experiments in "soil inoculation" have been carried out more or less 

 carefully in several places, chiefly by non-cultivators, but it is not possible 

 to draw any definite conclusions from them. But one thing at least appears 

 to have been demonstrated by experiments carried out by Professor Nobbe, 

 of Germany, and that is, that the nodule bacteria are likely to become 

 overfed and lazy if there is already a good supply of nitrogenous food 

 at their disposal in the soil; whereas, if there is a deficiency, it excites 

 them into greater activity and virulence, exactly as if they were millionaires 

 on the one hand and peasants on the other. 



The practical lesson to be learned from these investigations would 

 appear to be that (1) it would be a mistake to apply nitrogenous manures 

 to leguminous crops in any great quantity, as they would prevent the 

 healthy working of the bacteria; and (2) as the soil bacteria generally 

 are in greater numbers in the first six inches of soil, they could be utilized 

 to fertilize or inoculate the soil to a greater depth by trenching the soil, 

 and burying the top spit, containing the trillions of bacteria, lower down. 

 The subsoil rich in mineral foods (see p. Ill) but lacking in. bacteria, 



