CHAPTER V 

 ORGANIC MATTER 



A very important constituent of soil is the more or less 

 decomposed organic matter that has become incorporated 

 with it. Organic matter is found in larger quantity in sur- 

 face-soil than in subsoil because it comes largely from vege- 

 table matter that has fallen on the surface and there decayed, 

 or that has been plowed under. Animal remains and lower 

 forms of plant life also contribute to the supply. The roots 

 of dead plants are one source of organic matter, and as these 

 generally penetrate into the subsoil they deposit a limited 

 quantity of organic matter in that part of the soil. 



50. Classes of organic matter. — Organic matter that 

 is incorporated with soil gradually decomposes, forming 

 substances that are very different in their properties from 

 the original material. The process may be roughly divided 

 according to the degree of decomposition into three classes, 

 viz : (1) undecomposed matter, (2) partially decomposed 

 matter, (3) final products. The substances representing 

 each of the stages in the process have different properties 

 and differ in their effect on soil. 



Undecomposed organic matter is of use in making less 

 compact a heavy soil ; on the other hand, it may make too 

 loose a naturally light soil and may cause it to dry out to 

 such an extent that its productiveness will be curtailed. 

 For instance, a stand of oat stubble or of corn stalks that 

 would be of much benefit to a heavy soil in a humid region 

 might injure seriously a light soil in a semi-arid region. 



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