EXERCISE A-19. A STUDY OF SOIL TEMPERATURE. 



Equipment: Two or more thermometers; a soil auger. 



Method: For this exercise select a bright clay about 

 the time spring plowing begins. Go to a nearby field 

 and take the temperature by burying the bulb of the ther- 

 mometer to the depth of three inches. To avoid breaking 

 the thermometer, first make a hole in the soil to the proper 

 depth with a small stick or lead pencil and then insert 

 the thermometer. The reading should not be taken until 

 after the thermometer has been in contact with the soil 

 about fifteen minutes. While waiting to make this read- 

 ing, bore a hole to the depth of three feet and lower the 

 other thermometer until the bulb rests on the bottom. 

 At the end of fifteen minutes the thermometer should be 

 drawn to the top and read immediately. Take the tem- 

 perature at the three-inch depth, (1) of a north and of a 

 south slope; (2) of unplowed and freshly plowed land; (3) of 

 grass land and a cultivated field. Record all temperatures 

 and discuss the results. 



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