CHAPTER II. 



MANURES. 



Most Valuable Elements in Manures. — While there are 

 twelve or raore elements that enter into the composition of our 

 cultivated plants, yet only nitrogen, phosphorus and potash, 

 and in a few cases lime, are lacking from our agricultural soils. 

 These three elements enter largely into all our cultivated crops 

 and are necessary for their growth. The other elements are 

 usually present in abundance. 



Humus. — While humus in itself is not a plant food, it is of 

 great importance in the soil. It is formed by the decay of 

 organic matter and is composed principally of carbon. It 

 promotes chemical action by which plant food is set free in 

 the soil, and it increases the power of the soil for holding the 

 water and gases which it gives up slowly to the roots of 

 plants. Rotten stable manure contains a large amount of humus- 

 forming materials, which undoubtedly add very much to its 

 value, and it is probably on this account that it often gives 

 better returns than commercial fertilizers containing the same 

 quantities of what are termed the essential elements. 



The Action of Manures in the Soil can be and generally 

 is both direct and indirect. They act directly when they con- 

 tain actual available plant food or when by their decay they 

 yield it to the plant; they act indirectly when they start chem- 

 ical action in the soil and thus set free soluble plant food in 

 the soil itself. Almost all manures act in this indirect way to 

 some extent. A moderate application of stable manure by its 

 decomposition (which is chemical action) in. the soil has been 

 known to increase the temperature of the soil by three degrees. 

 Lime in itself is a plant food and is largely used by some crops. 

 Most soils, however, contain it in great abundance, yet if quick 

 lime be added to a soil already rich in common limestone it 

 generally serves to increase growth. This is not due to the 

 plant taking up more lime, but rather to the fact that the 

 quick lime starts chemical action in the soil by which some 



