ORGANIC MATTER 57 



(3) The soil should not lack lime, as the presence of lime 

 in a readily soluble form favors the development of many 

 forms of life that decompose organic matter, and it also 

 prevents the poisonous action of certain substances pro- 

 duced in the process. 



61. Sources of organic matter. — In addition to the 

 natural supply of organic matter referred to in the first part 

 of this chapter, there are other sources from which the 

 farmer may obtain a supply by outright purchase or by 

 means of their production on the farm. Among these are 

 farm manure, grass and clover sod, green-manures, peat and 

 muck, crop residues, like straw, cornstalks and leaves, dead 

 animals, certain commercial products, like cottonseed meal 

 and dried blood, and finally weeds, which are sometimes used 

 for that purpose in orchards. 



These various materials and their use in contributing to 

 the supply of organic matter in soils will be discussed later 

 under the respective heads (1) farm manure, (2) green- 

 manures and (3) commercial fertilizers. 



QUESTIONS 



1. Into what three classes may the organic matter of the soil be 

 divided ? . 



2. What is the effect of organic matter on the water-holding 

 capacity of soil ? 



3. What is the effect of organic matter on drainage ? 



4. How does organic matter contribute to the availability of 

 plant nutrients in soils ? 



5. In what general way does organic matter affect the growth of 

 bacteria in soils ? 



6. How do the final products in the decomposition of organic 

 matter increase the availability of plant-food materials in soil ? 



7. In what two ways may organic matter be injurious to soils ? 



8. What are the soil conditions that favor a rapid and desirable 

 decomposition of organic matter ? 



9. Name the sources of organic matter that may serve to increase 

 the supply in soils. 



