Liebig's Principle Refuted. 187 



period. The increased amount of nitrogen in the produce 

 is only about 45 per cent, of that supplied ; and the increase 

 of mineral matter removed is not much more than half as 

 much as would be contained in 1 ton of hay. 



It is clear, then, that the annual supply of not only the 

 mineral constituents, but the nitrogen also, of 1 ton of hay> 

 yielded less than two-thirds instead of 1 ton of increase 

 of produce; moreover, the character of the, herbage was 

 materially modified. The gramineous herbage was much 

 increased, the leguminous much reduced. 



The chief interest of this plot lies, perhaps, in the circum- 

 stance of its putting to the test the principle enunciated by 

 Liebig, and quoted above. Liebig, in his earlier writings, 

 did not recognise the fact that a considerable proportion of 

 the constituents removed from the land in crops is, in the 

 actual practice of agriculture, periodically returned to it, 

 and that, therefore, the loss to the soil is not measured by 

 the amount of constituents in the crops grown, but more 

 nearly by that in the produce sold off the farm. Further, 

 his recommendations for the carrying out of his principle 

 were confined to the application of the " mineral " or asJi- 

 constituents ; he maintaining that the atmosphere would 

 supply the necessary nitrogen. It is true that, subsequently, 

 in the course of controversy, he changed the meaning of his 

 terms, and then included ammonia- salts in the category of 

 mineral manures. It is seen, however, that even with a supply 

 of the amount of nitrogen, as well as ash-constituents, con- 

 tained in 1 ton of hay, not two-thirds of a ton of increase of 

 produce was obtained. 



With regard to the applicability of Liebig's principle, 

 certain considerations must not be overlooked First, there 

 is no conceivable condition of chemical combination, and of 

 distribution within the soil, in which the various constituents 

 could be annually supplied so as to be all annually taken up 

 by growing vegetation ; and there is conclusive evidence that, 

 in some cases, the unrecovered residue is, in greater or less 



