34 THE CHEMISTRY OF THE FARM. 



ingredient of plant food. The little value which salt pos- 

 sesses as a manure is probably due to its action in the soil, 

 where it may help to set free more important constituents. 



Application of Manures. — A manure can be efficacious 

 only when its constituents are brought into contact with 

 the roots of the crop. To obtain this contact to the fullest 

 extent the manure must be thoroughly and evenly dis- 

 tributed throughout the depth of soil mainly occupied by 

 the roots. Soluble manures — as nitrate of sodium, chlo- 

 ride of sodium, ammonium salts, potassium salts, and 

 superphosphate — have the great advantage that they dis- 

 tribute themselves within the soil after the first heavy 

 shower far more perfectly than can be done by any mode 

 of sowing. When manure is especially required by the 

 plant in its earliest stages — as superphosphate for turnips 

 — it may be drilled with the seed ; but, as a rule, manure 

 should be sown broadcast, and ploughed in or harrowed. 



Top-dressing, that is sowing manure on the surface of 

 land already under crop, should generally be confined to 

 manures that are soluble, or the principal constituents of 

 which easily become soluble in the soil. Nitrate of sodium 

 is sown with advantage in this manner if showery weather 

 can be depended on to distribute the manure in the soil. 

 On pasture all manures are necessarily applied as top- 

 dressings. 



Whenever possible, manure should be reduced to a fine 

 powder before application. Artificial manures, if distri- 

 buted by hand, should first be made up to a considerable 

 bulk by mixing with fine dry soil or ashes. Manures con- 

 taining ammonia must not be mixed with alkaline ashes, 

 else some of the ammonia will be lost. 



