4S ^ REPORT 1851. 



authors suggested that liere was an important field of study, and that we have in the 

 facts alluded to, much that should lead us to suppose, that the success of a rotation of 

 crops depends on the degree in which the restoration of the balance of the organic 

 constituents of crops was attained by its means rather than on that of their mineral 

 constituents according to the theory of Liebig ; whilst the means adopted to secure 

 the former were always attended with a sufficient supply of the latter. Again, Pro- 

 fessor Liebig had quoted the protesses of fallowing and liming, as being in their known 

 results inconsistent with the views of Mr. Lawes and Dr. Gilbert ; but these gentlemen 

 considered that the experiments of Mulder, and especially of Mr. Way on the pi-oper- 

 ties of soils, justified them in supposing that the process of fallowing and even that of 

 liming also owed its efficacy, more to the accumulation of nitrogen in the soil from 

 natural sources, than to that of available mineral constituents : the latter did, however, 

 undoubtedly thus accumulate by these processes, and this fact should give more con- 

 fidence in views, which on independent evidence supposed, that they were not so easily 

 liable to be found in defect in relation to other necessary supphes. 



It was next shown, by reference to what happens in actual practice, as generally 

 followed in Great Britain, that where corn and meat constitute almost the exclusive 

 exports of the farm, the mineral constituents of the crops, taken collectively, that is, 

 as shown by the analysis of their ashes, could not be considered as exhausted. Indeed 

 Baron Liebig himself states that farm-yard manure was the universal food of plants. 

 And the authors would draw attention to the fact, that the practice of agriculture here 

 supposed necessitated the production of this manure, by means of which it was that so 

 large a proportion of the mineral elements of the crops raised upon the land were, in due 

 time, restored to it. All our calculations therefore should be made on a full considera- 

 tion of what was involved in the use of farm-yard manure. This was however not 

 generally sufficiently borne in mind by chemists unconnected with practical agricul- 

 ture ; and to this cause might in great part be attributed the reiterated recommenda- 

 tions to imitate in artificial manures the composition of the ashes of the plants to be 

 grown. Of the mineral constituents however, phosphoric acid would be lost to the 

 farm (by the sales of corn and meat) in much larger proportion than the alkalies, 

 whilst the latter would generally, by the combined agencies of disintegration of the 

 native soil and import in cattle food, be liable to diminution in but a very insignificant 

 degree, if not in some cases to accumulation. Practical agriculture had, indeed, de- 

 cided that phosphoric acid must in most cases be returned to the land from sources 

 external to the farm itself, viz. by bones, guano or other means ; while, on the other 

 band, artificial alkaline manures had generally been found to fail in effect. 



Indeed, taking into careful consideration the tendency of all experience in practical 

 agriculture, as well as the collective results of a most laborious experimental investiga- 

 tion of the subject, both in the field and in the laboratory, it was the deliberate opi- 

 nion of the authors that the analj'sis of the crop was no direct guide whatever as to the 

 nature of the manure required to be provided in the ordinary course of agriculture, from 

 sources extraneous to the home manures of the farm, that is to say, by artificial manures. 



In conclusion, then, if the theory of Baron Liebig simply implied that the growing 

 plant must have within its reach a sufficiency of the mineral constituents of which 

 it is to be built up, the authors fully and entirely assented to so evident a truism : 

 but if, on the other hand, he would have it understood, that, in the ordinary course of 

 agriculture in Great Britain, it is of the mineral constituents as would be collectively 

 found in the ashes of the exported produce that our soils became deficient, relatively 

 to other constituents, they did not hesitate to say that every fact with which they were 

 acquainted in relation to this point was unfavoiU'able to such a view. On the con- 

 trary, they believed that nitrogen was the constituent most exhausted relatively to 

 other constituents ; at any rate, it was certain that for wheat, of all our crops, no sup- 

 ply of minerals, phosphates, &c. to the fields of Great Britain, woidd enable it to 

 "obtain a sufficient supply of ammonia from the atmosphere;" and indeed, that any 

 increased produce of it, such as British agriculture (itself so artificial) demands, could 

 not be obtained indejjendently of an artificial accumulation of mixogenwithin the soil. 

 If, however, a cheap source of ammonia were at command, the available mineral con- 

 stituents might in their turn become exhausted by its excessive use. Of those crops 

 of rotation, on the other hand, where the effect of mineral manures was characteris- 

 tically to increase the assimilation of nitrogen from atmospheric sources, and by virtue 

 of which property they indeed become subservient to the increased growth of grain, 

 the apparent demand for those substances, was not only generally, not such in hind, 



