DIFFERENT FORMS OF NITROGEN IN THE SOIL. 291 



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 

 assumptioiAhat the nature of nitrogen was as variable 

 in the arable soil as in manures ; one portion was sup- 

 posed 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 in- 

 effective. 



Hence 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 

 facts in support of this extension of it. They believed 

 that they could establish their point in the following 

 way. 



When a crop contained in corn and straw as much 

 nitrogen as was equivalent to six, four, three, or two 

 per cent, of the whole quantity of nitrogen in the soil, 

 the reason was that there were present in the field six, 

 four, three, or two per cent, of active nitrogen, while 

 the remaining 94, 96, 97, or 98 per cent, were inoper- 

 ative nitrogen. 



The cause of the effect (the amount of active nitro- 

 gen in the soil) was consequently inferred from the 

 effect (the amount of nitrogen in the crops). If more 

 of the whole quantity of nitrogen was in an active form, 

 then higher crops would follow ; if the crops were lower, 

 the reason was that there was a deficiency of active 

 nitrogen. If in guano or farm-yard manure additional 

 active nitrogen was supplied, the crops' would be in- 

 creased. 



By taking a new standard for estimating the pro- 

 ductive power of the soil, the former one for the valu- 



