Grade. 

 Date. . 



(74) 



EXERCISE 28 



Amount of Organic Matter in Soils 



Purpose. — To compare roughly the relative amounts of organic matter in 

 two different samples of field soils. 



1. Place a small amount of each soil in an evaporating dish and heat for 



several hours in an oven in order to drive off hygroscopic moisture. 



2. Number and carefully weigh on sensitive balances two or more crucibles 



with covers. 



3. Place in each crucible ten grams of the previously dried soil and ignite 



at a glowing temperature for an hour. Lift the cover occasionally to allow 

 gases to escape. 



4. After the samples have been cooled in a closed chamber, weigh again and 



determine the loss of each. 



5. The loss in weight of each sample is largely due to the burning away of 



the organic matter. A part of the loss is due, however, to the escape of 

 water, of crystallization, etc. 



6. Students having time for extra laboratory practice should test other 



samples for organic matter. 



Results 



Weight, crucible and soil 



Weight 

 crucible 



Before ignition 



After ignition 



Lo.ss, per cent 



QUESTIONS 



1. Do uplands or lowlands usually contain the most organic matter? Wh}^? 



2. Is the percentage of organic matter present in any soil a good indication 



of its fertility? 



3. Do soils containing much organic matter plow easier or harder than others? 



4. What is meant by active and inactive organic matter and what is their 



relative importance? Give examples of each. 



