36 Practical Farming 



tinguished as sandy loams and clayey loams according as 

 the soil particles differ in size and the soil is more or less 

 easy of cultivation. Soils derived mainly from the decay 

 of organic matter form a class by themselves, and are 

 termed peaty, swampy, or humus soils. These soils when 

 well drained are generally found to be abundantly sup- 

 plied with nitrogen, but are apt to be deficient in the min- 

 eral matters, phosphorus and potassium, and produce a 

 rank growth without a corresponding maturity of the 

 grain or fruit. 



One of the most important contents of arable soil is 



what we call humus, the decay of organic matter which 



makes the surface of the soil darker in 



Humus, Its color, more mellow in character, and above 

 Sources and . - . 



Services ^^^y raoxG^ retentive of moisture. While gen- 



erally esteemed of the greatest importance, 

 humus is still, in its chemical composition, not so well 

 understood as the mineral soils. Its value does not seem 

 to Ue so much in its furnishing plant food, though of course 

 it does this, as in its physiological and mechanical effect. 

 The soils of arid regions, which are generally deficient in 

 humus, are still very productive when only water is ap- 

 plied; and a soil of good mechanical composition will 

 produce fine crops though destitute of humus, if well sup- 

 plied with soluble plant food. 



Humus is formed from matter which once carried life, 

 either animal or vegetable, and which the forces of nature 

 are reducing to such form that the materials can be again 

 used in the building up of plants and the support through 

 them of animal life. It is simply the result of the never- 

 ceasing round by which nature uses over and over again 



