CHAPTER XIV 



ORGANIC MATTER AND NITROGEN 



THE organic matter of the soil may be considered in two classes, 

 active and inactive, although no very sharp line can be drawn 

 between them. 



The most active organic matter consists of such substances as 

 decaying plant roots and crop residues, green manures and animal 

 manures, incorporated with the soil. These products decay rapidly 

 in the soil and in the process of decomposition liberate not only 

 plant food which they contain, including nitrogen, phosphorus, 

 and potassium, but they also set free other decomposition products, 

 such as carbonic acid, nitric acid, and organic acids, which have 

 power to dissolve more or less additional plant food from the 

 mineral part of the soil. 



The inactive, or less active, organic matter consists of the more 

 resistant organic residue that remains after several years and that 

 decomposes very slowly. If present in large quantity, its gradual 

 decomposition may still supply sufficient nitrogen to meet the 

 needs of good crops, although its power to liberate mineral plant 

 food from the soil may not provide adequate supplies of available 

 phosphorus, potassium, etc. 



Thus, we find that one soil may at the same time be richer in 

 organic matter and less productive than another soil, even though 

 the two soils are alike in other respects. Three tons per acre of 

 fresh, actively decaying organic matter may be more effective 

 for a year or two than thirty tons of old and less active humus. 



The term humus is not synonymous with organic matter. 

 Humus includes only that part of the organic matter that has 

 passed the most active stage of decomposition and completely lost 

 the physical structure of the materials from which it is made, and 

 has thus become, as a rule, thoroughly incorporated with the soil 

 mass. 



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