CHAPTER III. 



MANURES. 



While there are twelve or more 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 large- 

 ly into all our cultivated crops and are necessary for their 

 growth. The other elements are usually present in abundance. 



Humus. — Humus, while not in itself a plant food, 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 yields up slowly to the roots of 

 the 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 con- 

 taining 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 

 chemical action in the soil and thus set free soluble plant 

 food in the soil itself. Almost all manures act in this in- 

 direct 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 large- 

 ly used by some crops. Most soils, however, contain it in 

 great abundance, yet if quick lime be added to a soil al- 

 ready rich in common limestone it generally serves to in- 

 crease 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 of the locked-up stores of 



