Agricultural Chemistry — Turiiips. 



495 



should tend to explain and to enforce good old practices, rather 

 than to put forth those which are new and untried, the utility or 

 even the necessity of the application of science to the improve- 

 ment of our national agriculture will not be the less evident. 



The question with the agriculturist is not so much what are 

 the constituents which must exist in his soil for the growth of a 

 given amount of produce ? but what constituents or class of con- 

 stituents does this or that crop exhaust, relatively to another con- 

 stituent or class of constituents? Looking at the subject in this 

 point of view, we are of opinion that the increased growth of corn 

 may be considered to have a very intimate relationship to the 

 amount of nitrogen supplied to the soil : and since, owing to the 

 scarcity and high price of ammoniacal salts, or other direct nitro- 

 genous supplies, it is impossible to rely upon these sources, a 

 rotation of crops, and the importation of food for stocky come to 

 be not merely the only generally applicable, but the most eco- 

 nomical means of restoring fertility to the soil. Under such a 

 course for the special accumulation of nitrogen, it will be found 

 that there is always secured an abundant coincident supply of 

 mineral and carbonaceous substances, and hence the direct im- 

 portation of these latter substances is seldom necessary. 



The results of our experiments upon wheat and other plants of 

 the gramineous family have indeed shown, beyond a doubt, that 

 the character of the exhaustion which the soil suffers by their 

 growth is essentially and pre-eminently nitrogenous; and since 

 common usage bears ample testimony to the efficiency of alternate 

 cropping, it is to be supposed that an examination into the com- 

 position, habits, and sources of growth of the plants which enter 

 into a rotation, would bring to view important functional differ- 

 ences and peculiarities in the different plants, and such as should 

 give confidence in general principles and tend to improvement and 

 economy in practice. 



The greatly varying form and appearance of the various agri- 

 cultural plants, implying, as undoubtedly they do, essential 

 differences in their sources of nutriment, have led, from but 

 superficial observation of them, to erroneous assumptions regard- 

 ing the true office of certain plants in a course of agricultural 

 cropping. Thus it is by some maintained that the large surface 

 of leaf put forth to the atmosphere by the turnip, taken in con- 

 nexion with the general character and utility of the crop, be- 

 speaks an almost exclusive reliance upon the natural resources of 

 the atmosphere for its carbonaceous supply ; and the direct appli- 

 cation of nitrogenous manures has accordingly been recommended 

 with the view of favouring to the greatest extent the develop- 

 ment of leaf as a means of securing bulb. 



Again, agricultural plants have been arranged according to 



