294 Agricaltural Chemistry. 



their conversion into organic compounds were efficient or opera- 

 tive in greater quantity, during the same time, than in the other. 

 If we now suppose the atmosphere to supply to two fields, as 

 above, of unequal fertility, instead of the ordinary quantity, twice, 

 thrice, or four times as much ammonia and carbonic acid, and in 

 equal proportion to both fields, the produce will still be unequal ; 

 that of the fertile field will still be higher than that of the other, 

 and that in the same proportion as before, for the conditions of 

 fertility in these soils are, in both, the same in amount as they 

 formerly were. 



If the produce is greater, when the supply of carbonic acid and 

 ammonia is doubled, than with the ordinary supply, this can only 

 depend on the circumstance, that in both fields more of the ter- 

 restrial elements of nutrition have become soluble and available 

 in the given time. Experience teaches us that a fertile field, if 

 supplied with more ammonia than the air supplies, yields a 

 heavier produce. Experience teaches farther, that the increase 

 of produce, under these circumstances, in two fields of unequal 

 fertility, is not proportional to the increased supply of ammonia ; 

 that the produce of the one, for example, of a clay soil, is doubled 

 or trebled bv the simple addition of as much ammonia as was 

 already supplied ; while the produce of the other field, of equal 

 size, for example, of a sandy soil, is not increased, or not 

 materially increased, by the addition of twice or thrice as much 

 ammonia as was formerly supplied to it. 



Since the efficacy of the carbonic acid and ammonia supplied 

 to the soil always depends on the quality of the soil, it is easy to 

 understand that, even in the altered circumstances above sup- 

 posed, the amount of produce must always be proportional to the 

 quantity of the mineral elements of nutrition present in the soil, 

 in a soluble or available form. An excess of ammonia cannot 

 supply a deficiency of these mineral elements, nor convert a mis- 

 proportion among them into a due proportion. 



I have, in my book, subjected to examination the effect of an 

 increased supply of carbonic acid and ammonia in the soil, and I 

 have been led to an explanation of this action totally diffi^rent 

 from that generally adopted. 



Nothing appears, at first sight, more simple and obvious than 

 the opinion that the atmospheric elements of nutrition, when 

 artificially supplied to cultivated soils, as in humus and ammonia, 

 increase the produce, because they are available, directly and 

 immediately, as food for plants, and are actually thus taken up ; 

 but a closer investigation leads to the conclusion that this ex- 

 planation, as a general rule, cannot be the true one. 



The consideration of agriculture on the great scale shows, that 



