66 THE CHEMISTRY OF THE FARM 



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

 the fullest extent the manure must be thoroughly 

 and evenly distributed throughout the depth of soil 

 mainly occupied by the roots. Soluble manures — as 

 nitrate of sodium, chloride of sodium, ammonium 

 salts, potassium salts, and superphosphate — have the 

 great advantage that they distribute themselves 

 within the soil after the first heavy shower far more 

 perfectly than can be done by any mode of sowing. 

 Whenever possible, manure should be reduced to a 

 fine powder before application. Artificial manures, 

 if distributed by hand, should first be made up to a 

 considerable bulk by mixing with fine dry soil or ashes.' 

 Manures containing ammonia must not be mixed with 

 alkaline ashes or with Thomas' slag, else some of the 

 ammonia will be lost. When manure is especially 

 required by the plant in its earliest stages — as super- 

 phosphate for turnips — it may be drilled with the 

 seed; but, as a rule, manure should be sown broad- 

 cast, and ploughed or harrowed in. 



To;p dressing — that is, sowing manure on the surface 

 of land already under crop — should generally be con- 

 fined 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. 



Manures of little solubility, or those for which the 

 soil has a great retentive power, may be applied to the 

 land before the growing period of the crop commences. 

 Diffusible manures, on the other hand, should be 

 applied only when the crop is ready to make use of 



