204 MANURE 



' It is, then, by this ynthetic rather than by the nnalytic method that we have sought 

 our results : and in the carrying out of our object we have taken wheat as the type of 

 the cereal crops, turnips as the type of the root crops, and beans as the representative of 

 the leguminous corn crop most frequently entering into rotation ; and having selected 

 for each of these a field which, agriculturally considered, was exhausted, we have grown 

 the same description of crop upon the same land, year after year, with different chemical 

 manures, and in each case with one plot or more continuously unmanured, and one 

 supplied every year with a fair quantity of farmyard manure. In this way 14 acres 

 have been devoted to the continuous growth of wheat since 1843, 8 acres to continuous 

 growth of turnips from the same date, and 5 to 6 acres to that of leguminous corn crops 

 since 1 847. And of field experiments, beside these, which amount in each year to from 

 30 to 40 on wheat, upwards of 90 on turnips, and 20 to 30 on beans, others have been 

 made, viz. some on the growth of clover, and some in relation to the chemical circum- 

 stances involved in an actual course of rotation, comprising turnips, barley, clover, and 

 wheat, grown in the order in which they are here stated. 



' It may be stated, too, that in addition to these experiments on wheat, and the other 

 crops usually grown upon the farm, as above referred to, we have for several years been 

 much occupied also with the subject of the feeding of animals, viz. bullocks, sheep, and 

 pigs ; as well as in investigating the functional actions of the growing plant in relation 

 to the soil and atmosphere ; and in connection with each of these subjects much labo- 

 ratory labour has constantly been in progress. 



' The scope and object of our investigation has been therefore to examine in the field, 

 the feeding-shed, and the laboratory, into the chemical circumstances connected with 

 the agriculture of Great Britain in its four main features ; namely 



' First, the production of the cereal grain crops ; secondly, that of root crops ; thirdly, 

 that of the leguminous corn and fodder crop ; and, fourthly and lastly, that of the con- 

 sumption of food on the farm, for its double produce of meat and manure. 



' So much then for the rationale and general plan of the experiments themselves, 

 and we now propose to call attention to some of the results which they have afforded us. 



' It is to field experiments on wheat that we shall chiefly confine our attention on 

 this occasion ; for wheat, which constitutes the principal food of our population, is 

 with the farmer the most important crop in his rotation, all others being considered 

 more or less subservient to it ; and it is, too, in reference to the production of this 

 crop in agricultural quantity that the mineral theory of Baron Liebig is perhaps 

 more prominently at fault than in that of any other. It is true, that in the case of 

 vegetation in a native soil manured by art, the mineral constituents of the plants being 

 furnished from the soil, the atmosphere is found to be a sufficient source of tho 

 nitrogen and carbon ; and it is the supposition that these circumstances of natural 

 vegetation apply equally to the various crops when grown under cultivation that has 

 led Baron Liebig to suggest that, if by artificial means we accumulate within the soil 

 itself a sufficiently liberal supply of those constituents found in the ashes of the plant, 

 essentially soil constituents, we shall by this means be able in all cases to increase 

 thereby the assimilation of the vegetable or atmospheric constituents in a degree 

 sufficient for agricultural purposes. But agriculture is itself an artificial process ; 

 and it will be found that, as regards the production of wheat more especially, it is only 

 by the accumulation within the soil itself of nitrogen naturally derived from the atmo- 

 sphere, rather than of the peculiarly soil constituents, that our crops of it can be 

 increased. Mineral substances will, indeed, materially develope the accumulation of 

 vegetable or atmospheric constituents when applied to some of the crops of rotation ; 

 and it is thus chiefly that these crops become subservient to the growth of the cereal 

 grains ; but even in these cases it is not the constituents, as found collectively in the 

 ashes of the plants to be grown, that are the most efficient in this respect ; nor can the 

 demand which we find thus made for the production of crops in agricultural quantity 

 be accounted for by the mere idea of supplying the actual constituents of the crop. 

 It would seem, therefore, that we can only arrive at correct ideas in agriculture by a 

 close examination of the actual circumstances of growth of each particular crop when 

 grown under cultivation. We now turn to the consideration of our experiments upon 

 this subject. It has been said that all the experimental fields were selected when they 

 were in a state of agricultural exhaustion. The wheat fields, however, after having 

 been manured in the usual way for turnips at the commencement of the previous 

 rotation, had then grown barley, peas, wheat, and oats, without any further manuring ; 

 BO that when taken for experiment in 1844, it was, as a grain-producer, considerably 

 more exhausted than would ordinarily be tho case. It was, therefore, in a most favour- 

 able condition for the purposes of our experiments. 



' In tho first experimental season, the field of 14 acres was divided into about 20 plots, 

 and it was by the mineral theory that we were mainly guided in the selection of 

 manures : mineral manures were therefore employed in the majority of cases. Ammonia, 





