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THE GENESEE FARMER. 



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prove the correctness of the above theory even though they gave no other m its place. 

 We conclude from these facts and others of a similar character, that the relative propor- 

 tion of any of the constituents of plants is in no case a certain indication of the relative 

 proportion in which these ingredients should exist in an available condition in the soil 

 or be supplied in manure. This can only be determined by inductive field experiments. 

 The theory we have adopted, though not so plausible as the one under discussion, is 

 far more in accordance with the observations and general practice of intelligent agricul- 

 turists, and we know of no well ascertained^ facts that throw doubt on its correctness. 

 It is in brief this : The principal requirement of the wheat and other cereal plants is 

 ammonia ; that of turnips, phosphates and carbon. Wheat destroys a large quantity 

 of ammonia during its growth, and collects its carbon from the atmosphere. Turnips 

 and clover, if supplied with available phosphates and carbon, collect their ammonia from 

 the atmosphere. The turnip crop contains a large quantity of nitrogen thus obtained 

 from the atmosphere. Its consumption on the land by animals destroys the greater 

 part of the carbon and abstracts considerable phosphoric acid, while nearly the whole ot 

 the nitrogen is left on the land in the excrements of the animals, and thus supplys the 

 following grain crop with the required ammonia as well as a large amount of potash 

 and other mineral constituents. The same remarks apply to the succeeding clover crop. 

 It collects its nitrogen from the atmosphere, and leaves it on the land m the roots ot the 

 plant and in the excrements of the animals consuming it, and so aflFords the indispensa- 

 ble ammonia for the following Avheat crop. 



We have considerable doubt in respect to agricultural plants collecting, to any great 

 extent, ammonia and carbonic acid from the atmosphere through their leaves. We are 

 inclined to think that what they obtain from the air is brought to the roots in rain. 

 The fact that broad-leaved plants obtain a large amount of organic matter from the air 

 in some way, is not necessarily opposed to our view, inasmuch as these plants, having 

 large surfaces exposed, evaporate a proportionably large amount of water, and so take 

 up more and with it imbibe more organic matter, which is retained m the plant. It has 

 been justly supposed that if plants obtained their organic matter from the atmosphere 

 throuo-h their leaves, a manure that would increase the size of the leaves would_ increase 

 the amount of organic matter obtained by the plant from the air, and enable it to dis- 

 pense with the organic matter of the soil. An ammoniacal salt apphed to the turnip 

 crop greatly increases the quantity of leaf per acre, but it does not increase the amount 

 of organic matter in either leaf or bulb, which should be the case did mcreased leaves 

 enable the plant to collect an increased quantity of organic matter from the air. On the 

 other hand, an application of superphosphate of lime, which greatly increases the under 

 ground collecting apparatus, or lateral fibrous roots, gives a very small proportion ot 

 leaf and a very large quantity and high proportion of organic matter m bulb and leat. 

 This would indicate that the power of agricultural plants to collect their food from the 

 air is dependent more on the extension of roots than on an artificial extension of leaves. 

 What we wish to be understood, therefore, when we say that plants of certain orders 

 collect their nitrogen from the atmosphere, is not that they inhale it cither as nitrogen, 

 ammonia, or nitric acid, through their leaves, but rather that they retain that which is 

 brought to them from the air in the rain water which they take up and evaporate. 



In our opinion, the whole theory of the English rotation of crops hangs on tl.e 

 destruction of ammonia during the growth of wheat and other cereals, and on the non- 

 destruction or retention of the ammonia by other orders of plants, such as the Cruciteroe 

 .and Leguminosa), and possibly of all plnnts containing but little silicic acid or starch. 

 If we admit the truth of this theory, and examine the effect of our too common system 

 of rotation— such as corn, barley, wheat, timothy, with perhaps a little clovca— we can 

 easily perceive that our soils would be sooner impoverished of nitrogen than of any other 

 element. This would not be the case if there was no destruction of ammonia during . , 



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