CHAPTER II. 



THE FERTILITY OF THE SOIL. 



The fertility of the soil is shown in the crops produced and a 

 soil is said to be fertile when profitable crops are grown under 

 favorable conditions. 



Composition of Soils. — In order to understand the conditions 

 which affect fertility let us become familiar with the composi- 

 tion of soils. Soils are made up of disintegrated (ground) 

 rocks and decayed plant and animal life. Some soils, like sandy 

 soils, predominate in rock particles while peaty soils are rich 

 in decayed plant material. Most soils contain both ground rocks 

 and decayed plants. 



Inorganic Matter. — That part of the soil composed of ground 

 rocks (sand, silt, clay, etc.) is called inorganic matter and 

 corresponds to some extent to the ash, or non-combustible, or in- 

 organic matter in plants. Of course the particles of inorganic mat- 

 ter in the soil may be different from the original rocks from which 

 they were derived, due to the action of rain, frost, sun, etc., yet 

 we find that a considerable portion of these particles is often of 

 the same composition as the original rocks. 



Organic Matter. — The decaying vegetable or animal matter in 

 the soil is called organic matter. It is that part of the soil 

 which is driven off when burned and corresponds to the organic 

 matter in plants. Most of the organic matter in soils comes 

 from decaying vegetation. When this decaying vegetable or animal 

 matter becomes thoroughly decomposed it assumes a black waxy 

 consistency and is called humus. This humus is a very im- 

 portant constituent and influences to a great extent the physical 

 and biological condition of soils. 



The amount of organic matter in soil influences its water hold- 

 ing capacity, texture, temperature, color, supply of available 

 plant food and general productiveness. 



Factors Influencing Soil Fertility. — There are many factors in- 

 fluencing soil fertility and these may be summed up under the 

 following heads : 



