DISTRIBUTION RENDERS FOOD EFFECTIVE. 95 



a cubic foot of earth, has no ^perceptible influence upon 

 its fertility ; but when uniformly distributed and phys- 

 ically combined with the minutest particles of the same 

 earth, it attains a maximum of efficacy. The influence 

 of the mechanical operations of agriculture upon the 

 fertility of a soil, however imperfectly the earthy parti- 

 cles may be mixed by the process, is remarkable and 

 often borders upon the marvellous. The spade, which 

 breaks, turns, and mixes the soil, makes a field much 

 more fruitful than the plough, which breaks, turns, and 

 displaces the earth, without mixing it. The effect of 

 both is increased by the harrow and the roller, so that, 

 in the very same places where a crop has grown during 

 the preceding year, a fresh crop will find nutriment ; in 

 other words, the earth is not yet exhausted. 



The action of chemical agents in distributing the 

 food-elements of plants is still more powerful than that 

 of the mechanical. By applying, in proper quantities, 

 nitrate of soda, salts of ammonia, and chloride of sodi- 

 um, the farmer not only enriches his field with materials 

 capable of taking part in the nutrition of plants, but he 

 also effects a distribution of the ammonia and potash, 

 thereby replacing or aiding the mechanical work of the 



E lough, and the influence of the weather in the time of 

 illow. 



We are in the habit of calling c manures ' all those 

 materials which, when applied to our fields, increase 

 the crops ; but the same effect is produced by the 

 plough. It is evident that the mere fact of a favour- 

 able influence exerted by chloride of sodium, nitrate of 

 soda, salts of ammonia, lime, and organic matter, 

 affords no conclusive proof that these have acted as 

 nutritive substances. The work performed by the 

 plough may be compared to the mastication of food by 

 those special organs with which nature has endowed 

 animals ; and nothing can be more certain than that 

 the mechanical operations of agriculture do not add to 

 the store of nutritive substances in a field, but that 

 they act beneficially by preparing the existing nutri- 

 ment for the support 'of a future crop. With equal 



