LITERATURE 101 



organic matter is not static but dynamic, being different from what 

 it was yesterday, and it will be different to-morrow from what it is 

 to-day, the changes being both qualitative and quantitative. The 

 soil organic matter gives off a constant stream of carbon dioxide, 

 diminishing from day to day, if the soil is left undisturbed. Rain 

 and dryness, heat and frost, will constantly modify the conditions 

 of the soil, influencing variously the activities of the microor- 

 ganisms, the nature and composition of the soil organic matter. 

 The nature of the growing plants and the management of the soil 

 still further modify the nature and amount of the soil organic 

 matter. That the organic matter of the soil which receives httle 

 or no added material becomes depleted is apparent from the fact 

 that about 30 mgm. of carbon dioxide may be produced per kilo- 

 gram of soil of average fertility every day for about 200 days of the 

 year. This would mean approximately a ton and a half of carbon 

 per year for each acre of 2,000,000 pounds. Boussingault stated 

 that in eleven years, one-half of the carbon in a certain soil had 

 been converted to carbon dioxide. 



A knowledge of the chemical composition of the plant and 

 animal residues undergoing decomposition, of the microorganisms 

 bringing about the decomposition of the various chemical con- 

 stituents, and of the environmental conditions under which the 

 decomposition is taking place, is essential before we can under- 

 stand the nature and rapidity of liberation of the nutrient elements 

 in forms available for plant growth and of the formation and 

 nature of the residual organic matter or soil humus. 



LITERATURE 



1. Buchanan, R. E., and Fulmer, Ellis I. Physiology and biochemistry of 



bacteria. Volume 2, Chapter 12; Volume 3, Chapter 18. The 

 WilUams & Wilkins Co. Baltimore, 1930. 



2. Lyon, T. L., and Buckman, H. O. The nature and properties of soils. 



Chapters 5 and 17. The Macmillan Co. New York, 1929. 



3. Proceedings and Papers of the First International Congress of Soil Science. 



Commission 3, Volume 3. Washington, 1928. 



4. Stephenson, M. Bacterial metabolism. Chapter 5. Longmans, Green 



and Co. London, 1930. 



5. Waksman, S. a. Principles of soil microbiology. Chapters 17, 19, 26. 



WiUiams & Wilkins Co. Baltimore, 1927. 



6. Waksman, S. A. Chemical nature of soil organic matter, methods of 



analysis, and the role of microorganisms in its formation and decom- 

 position. Transactions of the Second Commission of the Inter- 

 national Society of Soil Science. Part A, Budapest, 1929. 



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I L I 8 R A R Y 



