124 NATURE TEACHING. 



MANURING. 



1. Every crop taken off the land repre- 

 sents so much actual weight of nitrogen, phos- 

 phates and potash removed from the soil. 

 This fact is too often lost sight of in practice 

 and crops are removed, year after year, with- 

 out any attempt being made to keep up the 

 supply of food-stuffs in the soil. The plants 

 then draw upon the supply of food material 

 present in the soil, and thrive until this is no 

 longer able to satisfy their wants. The object 

 of manuring is to maintain this supply, or 

 even to increase it. 



2. Any method by which the fertility of 

 the soil can be increased may be included 

 under the general term manuring. Thus 

 thorough tillage of the soil, and the careful 

 maintenance of the conditions necessary for 

 the activity of the useful bacteria, are, in them- 

 selves, most important manurial operations. 

 At the present day, however, the word manure 

 is only applied to the actual substance added 

 to the soil. 



3. Manures may be classed according to the 

 substances they contain. Thus we have nitro- 

 genous manures, poto^sic manures, and phos- 

 phatic manures, which add, respectively, nitro- 

 gen, potash,, and .phosphates to the soil. 



