214 THE SYSTEM OF FARM- YARD MANURING. 



If two fields have tlie same abundance of straw-con- 

 stituents, but are not equally rich in corn-constituents, 

 the same supply of farm-yard manure will not produce, 

 by any means, equal crops of corn, because these must 

 bear a relation to the corn-constituents supphed in the 

 manure. Of these, both fields received the same amount 

 in the same quantity of manure ; but as the one field, of 

 itself, was richer in corn-constituents than the other, the 

 poorer of the two must receive much more manm^e to 

 make it produce as large crops as the other. 



A comparatively small quantity of superphosphate 

 will, on a field of the kind, serve to increase the produce 

 to a much greater extent, than the most liberal use of 

 farm-yard manure. 



Upon a field deficient in potash farm-yard manure acts 

 by the potash contained in it ; upon a soil poor in mag- 

 nesia or Hme, by its magnesia or lime ; upon one poor in 

 sihcic acid, by the straw in it ; upon land poor in chlo- 

 rine or iron, by the chloride of sodium, chloride of potas- 

 sium, or iron contained therein. 



This fact accounts for the high favour in which farm- 

 yard manure is held by practical farmers. As the dung 

 of the farm-yard contains, under all circumstances, a cer- 

 tain quantity of each of the mineral constituents with- 

 drawn from the soil by the crops grown on it, its action 

 is universally beneficial. It never fails to produce the 

 desired effect, and thus spares the practical man the 

 trouble of devising more suitable and equally efficacious 

 means for keeping up the fertility of his fields, with a less 

 profuse expenditure of money and labour, or of raising 

 his land, without additional outlay, to the highest attain- 

 able degree of fertihty compatible with its composition. 



It is well-known in practice, that the produce of many 

 fields may be increased by manuring with guano, bone- 



