22 SOIL CONDITIONS AND PLANT GROWTH 



explanation of the process had been offered, although the 

 discussion of rival hypotheses continued up till i860, but the 

 conditions under which it worked were known and on the 

 whole fairly accurately described. 



No connection was at first observed between nitrate 

 formation and soil productiveness. Liebig rather diverted 

 attention from the possibility of tracing what now seems an 

 obvious relationship by regarding ammonia as the essential 

 nitrogenous plant nutrient, though he admitted the possible 

 suitability of nitrates (174^:). Way came much nearer to the 

 truth. In 1856 (298;^) he showed that nitrates were formed 

 in soils to which nitrogenous fertilisers were added. Un- 

 fortunately he failed to realise the significance of this discovery. 

 He was still obsessed with the idea that ammonia was essential 

 to the plant, and he believed that ammonia, unlike other 

 nitrogen compounds, could not change to nitrate in the soil, 

 but was absorbed by the soil by the change he had already 

 described (p. 17). But he only narrowly missed making an 

 important advance in the subject, for after pointing out that 

 nitrates are comparable with ammonium salts as fertilisers he 

 writes : " Indeed the French chemists are going further, several 

 of them now advocating the view that it is in the form of 

 nitric acid that plants make use of compounds of nitrogen. 

 With this view I do not myself at present coincide : and it is 

 sufficient here to admit that nitric acid in the form of nitrates 

 has at least a very high value as a manure." 



It was not till ten years later, and as a result of work by 

 plant physiologists, that the French view prevailed over 

 Liebig's and agricultural investigators recognised the im- 

 portance of nitrates to the plant and of nitrification to soil 

 fertility. It then became necessary to discover the cause of 

 nitrification. 



During the sixties and seventies great advances were 

 being made in bacteriology, and it was definitely established 

 that bacteria bring about putrefaction, decomposition and 

 other changes ; it was therefore conceivable that they were 

 the active agents in the soil and that the process of decom- 



