120 THE PRINCIPLES OF SOIL MANAGEMENT 



a large amount of partially decayed leaves and stems, 

 sometimes termed leaf-mold. Sod land is filled with 

 fine roots, which have served their period of usefulness 

 to the plant and are being returned to their native 

 elements. The low swamp areas of soil contain a large 

 proportion of dark or black material, which, when the 

 soil is dry, may be burned away, and leaves the residue 

 a much lighter color. And in all soils there is some of 

 this same volatile material derived from the growth 

 and partial decay of plants and animals, and commonly 

 termed organic organized matter. 



Organic matter may be found in the soil in all stages 

 of decay, from the fresh tissues to the last oxidation 

 products of its components. These products of the var- 

 ious stages in the decay process, comprehended by the 

 term organic matter, constitute probably the most 

 important body of material which enters into normal 

 soil. 



52. Sources, derivation and forms. The organic 

 matter in the soil is derived from both plants and 

 animals: plants are the chief source. These materials 

 undergo decay through the action of bacteria and 

 fungi, in addition to purely chemical changes. The 

 character of the intermediate material depends largely 

 on the relative prominence of the different agencies 

 concerned in its decomposition. This great variety 

 in the material, together with the differences in pro- 

 cesses of decay, gives rise to a number of forms of or- 

 ganic material which are recognized in the soil. These 

 materials do not represent any definite composition. 

 They represent, rather, stages in the general process 



