Oil Agricultural Cliernidrij. 



245 



The superiority which Liebig's manure, when used alone, ex- 

 hibits, as compared with the result of the unmanured space, may 

 be attributed to its containing a small quantity of ammoniacal 

 matter, which was distinctly perceptible to the smell. 



The absolute necessity of supplying nitrogen to enable the soil 

 to produce more wheat than it could do in a natural state, is so 

 apparent throughout this series of experiments, that it is difficult 

 to entertain the slightest doubt upon the subject. As long as 

 any available ammonia exists in the soil, so long will mineral 

 manures increase the produce of wheat. If I had commenced 

 my experiments upon a field in high condition, full of animal and 

 vegetable matter, I might have been some years in arriving at the 

 true action of mineral manures : as it 'was^ the first year almost 

 decided the question. 



For the last seven years this field has suffered an immense loss 

 of minerals, rendered available to the plant by means of ammonia; 

 and the produce of last year (1846) showed that the mineral con- 

 dition was still little impaired. The crop now growing shows, 

 however, symptoms of an opposite condition of soil. In some 

 experiments, where no minerals have been supplied, the salts of 

 ammonia are not producing their accustomed effect: an excess of 

 the azotized condition is commencing, and mineral manures will 

 now have to be employed to increase the natural produce of the 

 soil. 



The various contradictory results obtained by the application 

 of mineral manures to wheat are completely accounted for when 

 it is known that they only increase the produce in proportion to 

 the available azotized matter existing in the soil. Although I 

 have confined my remarks to the wheat crop, they apply equally 

 to the whole class of plants belonging to the same '-'natural order," 

 Though they do not thrive equally well in the same climate and 

 soil, I consider them all to be plants in which the nitrogen sup- 

 plied in the manure is more than what is obtained in the produce. 

 They may for our present purpose be called nitrogen-consuming 

 plants, in contradistinction to those which are nitrogen-collecting 

 plants, and contain more of this substance than was supplied to 

 them in the manure. Common pasture belongs to the same class 

 of plants as our grain crops : hence we have an additional argu- 

 ment to the number already advanced, in favour of breaking it up 

 in every case where it is not required for ornamental purposes. 



The theory advanced by Liebig, that ''the crops on a field 

 diminish or increase in exact proportion to the diminution or in- 

 crease of the mineral substances conveyed to it in manure," is 

 calculated so seriously to mislead the agriculturist that it is 

 highly important its fallacies should be generally known. The 

 contempt which the practical farmer feels for the science of 



