420 The Neglect of Chemistry hy Practical Farmers. 



When we come to compare the balance left in the soil after these 

 two rotations, supposing the bean crop to have succeeded in both, 

 we find that with the green rje and turnips there is a larger defi- 

 ciency both of nitrogen and potash, that of the latter amounting 

 to 84 lbs. per acre ; or, in other words, the soil would have had to 

 supply 84 lbs. of potash, in addition to that supplied by the 

 manure, in order to grow a crop of beans, whereas in the rotation 

 where the rye was allowed to stand for seed, there was a large 

 excess of potash, and a sufficiency of nitrogen. 



The obvious deduction from the above calculation is, that the 

 bean crop failed after the turnip crop for the want of either 

 nitrogen or potash, or both combined, the soil not being able to 

 supply the deficiency ; but, nevertheless, I should hesitate to 

 assert it as a positive fact, unless confirmed by a number of 

 similar observations^ for it must be borne in mind, that we 

 cannot be too cautious of jumping to a conclusion in these matters, 

 particularly when we remember the comparatively imperfect 

 materials that are at present at our command for determining 

 fairly the average composition of every crop. 



I am sorry that it was not in my power to verify the truth of 

 the above deduction, by the application of some salts of potash 

 and ammonia^ both separately and conjointly ; but the land 

 coming in for green crops again, it was prepared by trenching 20 

 inches deep, which, of course, would prevent any fair deduction 

 from being drawn afterwards, whatever might have been the 

 result of the experiment. 



Some, perhaps, may object that these results are not to be 

 depended upon, inasmuch as the identical crops themselves were 

 not subjected to analysis, nor even their produce actually weighed; 

 but for my part, I think a general average analysis is quite as 

 likely to be correct for a whole acre as a single analysis, though 

 made of a plant growing upon that very acre. Of course, no 

 dependence can be placed upon a slight variation only, as all 

 the acreage quantities are but approximations to the actual weights. 

 I think, however, that a number of facts, exhibiting such marked 

 results as the above, when brought to bear on one another, would 

 probably be of some service, in enabling us to grope our way 

 along the obscure path of theory. 



Should, however, a greater degree of exactness be desired, we 

 may readily obtain it by burning a small given weight of the 

 crop, &c., and thereby calculating the actual amount of ash con- 

 tained in one acre of the crop, &c., whence we may easily estimate 

 the probable quantity of each individual ingredient contained in 

 that amount of ash. 



Again, as the labour of making direct experiments is very 

 great, and sufficient of itself to deter many farmers from interest- 



