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Rate of Humification of Manures. 



R. H. Carr. 



It has -been recognized for a long time that organic matter is an important 

 constituent of the soil, but as to just what way it aids in crop production, 

 there seems to be considerable difference of opinion. Some maintain that it is 

 valuable only for the plant food it carries, while others value it more espec- 

 ially for the plant food in the soil which may be made available by its decom- 

 position. The following paragraph from the Iowa Station, found in the 

 September, 1915, Journal of the American Chemical Society expresses the 

 sentiment of many soil investigators as to the value of humus, and the rate 

 of humification. "The organic matter extracted by alkali is of no very differ- 

 ent character than the organic matter of the soils as a whole. This together 

 with the fact proved by Fraps and Hammer, Texas Bui. 129, that upon add- 

 ing organic matter to soil, at the end of a years time there is no more material 

 extracted with diluted ammonia than at the beginning of the period, proves 

 quite conclusively that the determination of the amount of humus as found by 

 the various methods is of no particular value in the study of a soil." This 

 statement seems rather unreasonable to the author of this article, since the 

 elements that are of value as fertilizers are locked up in most farm manures, 

 green manures, cotton seed meal, etc., as complex compounds and hence are 

 unavailable to the growing plant which must have its food supplied in a very 

 simple form. In well rotted manures these complex molecules are largely 

 broken down to simpler substances containing the same elements, but with a 

 different arrangement in the molecule. They are quite soluble in water and 

 if not leached by rains are very effective as a fertilizer compared with fresh 

 manure. 



Therefore, since fertility is so closely related to the unlocking of these 

 complex plant molecules in the manures, an effort was made to measure the 

 rate of humification of the more common ones. 



Plan of Procedure. 



A clay soil was chosen that was very deficient in organic matter and was, 

 therefore, humus-hungry. With this soil were mixed different manures so 



