Fertility of Soils. 53 



totally different from that in the soil. The close relation 

 between the carbon and nitrogen, in the soils of plots 3 and 7, 

 indicates that the larger amount of nitrogen in plot 7 is not 

 due to the direct storing up of ammonia by the soil, but to the 

 nitrogen forming part of the vegetable growth, and being thus 

 stored up in the stubble and roots. If the nitrogen of the 

 ammonia-salts had been stored up in any form except that 

 of vegetable growth, the relation of carbon to nitrogen 

 would have been lower on plot 7 than on plot 3, instead 

 of which it is higher; there is also proof founded on 

 analyses of the soils of plot 7 and plot 3 that, of the two, 

 the latter contains by far the larger amount of unexhausted 

 fertility. 



The adjoining field, where barley is grown continuously, 

 furnishes similar evidence. For twenty consecutive years, 

 14 tons per acre of farmyard manure were applied to one plot 

 of barley, after which period the plot was divided into two, 

 the dung being continued on the one half, and stopped on 

 the other. Up to 1883, twelve unmanured crops had been 

 taken, yielding an average of 34J bushels per acre, and, as 

 the last of these crops, in the rather favourable season of 

 1883, exceeded 35 bushels, there is evidence of a long future 

 before the fertility due to the residue of the twenty years' 

 application of dung will be exhausted. In the same field the 

 plots manured with rapecake yield on analysis a considerably 

 larger amount of nitrogen than any of the plots where 

 minerals, or minerals with ammonia-salts or nitrate, have 

 been used. It follows that whilst fertility may be stored up 

 in the soil, in the form of such mineral substances as potash 

 or phosphate, it does not appear that the more valuable 

 substance, nitrogen, can be stored up unless combined with 

 carbon ; in other words, whilst the soil fixes potash and phos- 

 phoric acid independently of vegetation, nitrogen is only 

 fixed by the agency of vegetation. 



