DIFFEREXT FORMS OF NITROGEN IN THE SOIL. 307 



tioii of the per ccntage of nitrogen in the ground was no 

 longer of any use in estimating its productive power. 



This strange circumstance might well liave excited 

 suspicion against the theory of the preponderating influ- 

 ence of nitrogen, for which, as already observed, there is 

 not the slightest evidence in point of fact. But instead 

 of this, the advocates of the theory maintained it stead- 

 fastly, and endeavoured to explain the beliaviour of the 

 soil upon new and still more extraordinary grounds. It 

 had been observed that a very small fraction of the quan- 

 tity of nitrogen present in the soil, in the form of guano, 

 farm-yard manure, or nitrate of soda, materially increased 

 the crops ; whereas, the effect of other manures, which 

 contained nitrogen not in the form of ammonia or nitric 

 acid, was very unequal in respect of time, and, in the case 

 of horn shavings or woollen rags, was extremely slow. 

 This led to the assumption that the nature of nitrogen 

 was as variable in the arable soil as in manures ; one 

 portion was supposed to be in the form of ammonia or 

 nitric acid, and this was, properly speaking, the effective 

 part ; another portion, on the contrary, existed in some 

 peculiar form which could not exactly be defined, and was 

 quite ineffective. 



Ilence the productive power of a soil was, according to 

 this view, not in proportion to the entire quantity of 

 nitrogen in it, but could only be measured by the nitric 

 acid and ammonia which it contained. As the advocates 

 of the theory about the effective operation of nitrogen had 

 been accustomed to shirk proving the truth of their 

 doctrine, as a matter of course they did not trouble 

 themselves about adducing any positive fiicts in support 

 of this extension of it. They beheved that they could 

 establish tlieir point in tlie following way. 



When a croj) contained in corn and straw as much 



X 2 



