38 



On Agricultural Chemistry. 



experience of fallow is sufficient to show the fallacy of our opi- 

 nions ; but in this very process^ and that even of liming also, when 

 rightly considered, we believe we see that which should give con- 

 fidence in the views we have maintained. It cannot be doubted 

 that by the processes of fallowing and liming, the disintegration 

 of the minerals of the soil, and the increase of the available supply 

 therefore of their several constituents, must thereby be enhanced. 

 But notwithstanding we have in the direct experiments of Wieg- 

 mann and Polstorffj of Rogers, and others, sufficient evidence of 

 such disintegration under the action of air and water ; yet there 

 is, in our opinion, equal reason for believing that the processes of 

 fallowing and liming owe their efficacy, as much or more to the 

 changes which take place within the soil in regard to the available 

 supply of the nitrogen which plants require, as of their purely 

 mineral constituents. Thus Professor jMulder has concluded that 

 the organic acids of the soil which he has investigated, have the 

 power of accumulating ammonia from the atmosphere. Now 

 these compounds will only be retained within the soil where 

 organic matter is subject to a very slow process of decomposition, 

 and it is precisely in the heavier soils, where the processes of 

 fallowing and liming are found to be most beneficial, that organic 

 matter will be shut up and subject to a very slow decomposing 

 action, which these processes will materially assist. But more 

 important still; — the experiments of Mr. Way on the absorptive 

 properties of soils have directly proved, what was before indeed 

 supposed, that it is the heavier soils, those again therefore that 

 are most influenced by fallowing and liming, that possess in the 

 highest degree the power of absorption and retention of ammonia 

 and other substances, to the action of which they may be exposed. 

 We do not, indeed, mean to say that the processes in question owe 

 their value entirely to the influence of the actions to which we 

 have alluded ; but we think it may reasonably be suggested that 

 there is, at least, as much evidence in favour of this view of 

 the efficacy of fallov/ing more especially, as in the mineral theory 

 of it ; and the more so when we remember that it is the wheat 

 crop, for which nitrogen in the soil is found to be so important, 

 that almost invariably succeeds the fallow. And the fact that 

 mineral substances do at the same time accumulate, should itself 

 give confidence in views which, on independent grounds, suppose 

 that they are not so easily liable to be found in defect in relation 

 to other necessary supplies. 



Reviewing, then, the actual facts of practical agriculture, as 

 generally followed in Great Britian, we have seen how small is 

 the utmost annual loss of alkalies under the export of corn and 

 meat alone, and that the demand thus made upon the stores of 

 the native soil will generally be truly insignificant. Phosphoric 



