MANURE 203 



much wider range than this), and taking the one constituent of ammonia or nitrogen as 

 an illustration, that in adding to this quantity of soil a quantity of ammoniacal salt, con- 

 taining 100 Ibs. of ammonia, which would be an unusually heavy and very effective 

 dressing, we should only increase the percentage of ammonia in the soil by 0007, it 

 is evident that our methods of analysis would be quite incompetent to appreciate the 

 difference between the soil before and after the application, that is to say, in its state 

 of exhaustion, and of highly productive condition, so far as that constituent is con- 

 cerned ; and, from our knowledge of the effects of this substance on wheat, we may 

 confidently assert that the quantity of it supposed above would have given a produce 

 at least double that of the unmanured land. The same kind of argument might, indeed, 

 be adopted in reference to the more important of those constituents of a soil which are 

 found in the ashes of the plant grown upon it, and we determined, therefore, to seek 

 our results in another manner. Indeed, the imperfection of our knowledge of the pro- 

 ductive quality of a soil, as derived from its percentage composition, has been amply 

 proved by the results of analysis which have been published during the last ten years ; 

 and in corroboration, we need only refer to the opinions of Professor Magnus on this 

 subject, who, in his capacity of chemist to the 'Landes-Oekonomie Kollegium ' of 

 Prussia, has published the result of many analyses of soils. The truth is, that little is 

 as yet known of what a soil either is, or ought to be, in a chemical point of view ; but 

 when we call to mind the investigations of Professor Mulder in relation to the organic 

 acids found in soils, and of Mr. Way and others as to the chemical and physical pro- 

 perties of soils in relation to the atmosphere and to saline substances exposed to 

 their action in solution, we may at least anticipate for chemistry that she will ere 

 long throw important light on this interesting but intricate subject. 



' In our field experiments, then, we have been satisfied with preserving specimens of 

 the soils which were to be the subjects of them, and have sought to ascertain their de- 

 ficiency, in regard to the production of different crops, by means which we conceive to 

 be not only far more manageable, but in every way more conclusive and satisfactory in 

 their result. To illustrate : What is termed a rotation of crops is at least of such 

 universality in the farming of Great Britain, that any investigation in relation to the 

 agriculture of that country may safely be grounded on the supposition of its adoption. 

 Let us, then, direct attention for a moment to some of the chief features of rotations. 

 What is called a course of rotation is the period of years which includes the circle of 

 all the different crops grown in that rotation or alternation. The crops which thus 

 succeed each other, and constitute a rotation, may be two, three, four, or more, varying 

 with the nature of the soil and the judgment of the farmer ; but whatever course be 

 adopted, no individual crop wheat, for example is grown immediately succeeding 

 one of the same description, but it is sown again only after some other crops have 

 been grown, and at such a period of the rotation, indeed, as by experience it is known 

 that the soil will, by direct manure or other means, have recovered its capability of 

 producing a profitable quantity of the crop in question. 



' On carefully considering these established and well-known facts of agriculture, 

 it appeared to us that, by taking soils either at the end of the rotation, or at least at 

 that period of it when in the ordinary course of farming farmyard manure would be 

 added before any further crop would be grown, we should then have the soils in what 

 may be termed a normal, or, perhaps better still, a practically and agriculturally 

 exhausted, state. 



' Now, if it is found, in the experience of the farmer, that land of any given qua- 

 lity, with which he is well acquainted will not, when in this condition of practical 

 exhaustion, yield the quantity he usually obtains from it of any particular crop, but 

 that after applying farmyard manure it will do so, it is evident that if we supply to 

 different plots of this exhausted land the constituents of farmyard manure both indi- 

 vidually and combined, and if by the side of these plots we also grow the crop both 

 without manure of any kind and with farmyard manure, we shall, in the comparative 

 results obtained, have a far more satisfactory solution of the question as to what con- 

 stituents were, in this ordinary course of agriculture most in defect in respect to the 

 proportion of the particular crop experimented upon, than any analysis of the soil 

 could have given us. In other words, we should have before us very good ground 

 for deciding to which of the constituents of the farmyard mannro the increased pro- 

 duce was mainly due on the plot provided with it, in the case of the particular crops : 

 not so, however, unless the soil had been so far exhausted by previous cropping as to 

 be considered practically unfit for the growth of the crop without manure. We lay 

 particular stress on this point, because we believe that the vast discrepancy in the 

 results of comparative trials with different manures, by different experiments, arises 

 more from irregularity in what may be called the floating capital of the soil, than from 

 irregularities in the original character of the soil itself, or from any other cause, 

 unless we include the frequent faulty methods of application. 



