228 



On Agricultural Chemistry. 



obtaining them in sufficient quantity for their use. The great 

 problem to be solved with regard to manures is, what substances 

 is it necessary to supply to the soil in order to maintain a re- 

 munerative fertility ? The solution of this question appears easy 

 enough, regard being had only to the composition of the crops 

 removed. Practically there are, however, great difficulties attend- 

 ing it, which can only be entirely overcome by a long series of 

 careful and costly experiments. If the ash theory advanced by 

 Liebig, and so industriously propagated by his pupils, were 

 founded on truth, a careful examination of the ashes of plants, and 

 a few simple calculations upon the amount of mineral substances 

 exported from the soil in corn, meat, &c., would at once enable 

 us to explain and remedy the exhaustion of our soils. The 

 farmer, when he sends his load of wheat to market, would bring 

 back the few pounds of minerals which the wheat contained, and 

 the return of these to the soil would enable him to produce the 

 same amount of w^heat for the market the following year. Un- 

 fortunately, however, the ground-work upon which this theory is 

 raised is unsound, when agriculture, as distinguished from natural 

 vegetation, forms the subject of consideration. 



Agricultural plants, which practice has shown to differ widely 

 from each other in their respective relations to soil, climate, 

 manuring, and position in rotation, possess at the same time 

 widely differing powers of reliance upon the atmosphere for the 

 constituents which it is known to supply in a greater or less de- 

 gree. If grain crops held the same relation to natural and arti- 

 ficial supply of their organic constituents, as thejeguminous plants 

 and turnips, the farmer would not require the assistance of the 

 latter crops ; but since, compared with these, the grain crops are 

 in some important respects far more dependent upon artificial 

 supply to the soil of certain organic constituents, of which the 

 price is high and the supply limited, it becomes necessary to 

 employ certain plants which possess the power of collecting these 

 ingredients from the atmosphere, and such procedure constitutes 

 a rotation of crops. 



For some years past I have been engaged in a very extensive series 

 of experiments upon my farm, with a view to determine some of 

 the more important questions which are constantly arising in the 

 minds of agriculturists. It would be impossible in a paper of 

 this description to enter into a detail of the plan I have pursued 

 in conducting these experiments. Keeping in mind the motto of 

 the Society, ' Practice with science' I shall now merely select 

 those results which bear most upon practical agriculture, and 

 which appear to me most suitable to my present purpose. The 

 greater portion of these experiments, and the various points of 

 s^cience connected with them, will be discussed with more pro- 



