DISTRIBUTION EENDERS FOOD EFFECTIVE. 87 



phosphate of magnesia and ammonia is produced; but 

 this precipitate makes its appearance as soon as the 

 fermentation of the sap has destroyed tlie (azotised) 

 substance with which the phosphate of magnesia is com- 

 bined. 



Careful mixture and distiibution of the nutritive sub- 

 stances present in the soil, are the most important means 

 of rendering them effective. 



A piece of bone, weighing half an ounce, placed in a 

 cubic foot of earth, has no perceptible induence upon its 

 fertihty ; but when uniformly distributed and physically 

 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 fertihty of 

 a soil, however imperfectly the earthy particles 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 

 Avhere a crop has grown dming 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 applpng, in proper quantities, nitrate of 

 soda, salts of ammonia, and chloride of sodium, 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 plough, 

 and the influence of the weather in the time of fallow. 



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



