154 



SOILS AND FERTILIZERS 



First pull atmospheric air into the limewater for five minutes. 

 Note results. Now connect flask to tube extending into the soil and 

 draw in soil air. What conclusions do you come to regarding the 

 relative carbon dioxide content of soil air and atmospheric air ? 

 What is the function of carbon dioxide in the soil ? 



Exercise III. — Production of carbon dioxide by bacteria. 



Materials. — Flask, limewater and moist 

 rich soil. 



Procedure. — Place a small amount of 

 limewater in a flask and then suspend in 

 the flask over the limewater a bag of rich, 

 moist soil. Stopper tightly and allow to 

 stand for a week. Note the turbidity of the 

 limewater. Explain the results. 



Exercise IV. — Temperature and color. 

 Materials. — Coal dust and calcium hy- 

 drate. Thermometers. 



Procedure. — Divide a small plat of 

 smooth, level soil into three portions. 

 Leave one part untouched, cover one with a 

 thin coating of coal dust and the other with 

 a coating of calcium hydrate. On a warm, 

 sunny afternoon take the temperatures of 

 each at one, three and six inches deep. 

 Tabulate and give a practical explanation 

 of the data obtained. 

 Exercise V. — Slope and temperature. 

 Materials. — Thermometers. 



Procedure. — On a warm, sunny day take temperature at one, 

 three and six inch depths on a south slope, north slope and level 

 land, being careful to select for the observations soils having the 

 same texture and moisture contents. Tabulate data and explain 

 the practical relationships between temperature and slope of land. 

 Exercise VI. — Drainage and temperature. 

 Materials. — Soil, two jars, thermometer. 



Procedure. — Prepare two large jars of moist soil. Stir one until 

 two or three inches of the top soil is dry. Add water to the other 

 until it is saturated. Set these jars of soil in the sunshine out of 

 doors on a warm day. After two hours take the temperature of 

 the two soils at one inch and three inches in depth. Tabulate data. 



Fig. 28. — Production 

 of carbon dioxide by 

 germs in soil. (^4.) tight 

 stopper, (B) flask con- 

 taining limewater, (C) 

 small bag containing 

 moist soil suspended from 

 stopper, (D) limewater. 



