AGRICULTURE FOR SOUTHERN SCHOOLS. 



9 



difference between the net weight of the dry soil and that of the wet 

 soil is the weight of the water stored. During the time that the chim- 

 neys are dripping, which may be several days, they should be covered 

 to prevent evaporation of water from the surface of the soils. 



Record and report: A record should be made by each student of 

 the time and weights involved in each part of the exercise. A writ- 

 ten report should bring out the application of this test to the capacity 

 of different types of soils to take in and retain rainfall and irriga- 

 tion waters. The effects of plowing to loosen the soil and rolling to 

 pack it should also be brought out in their relation to the water- 

 holding capacity of soils. 



Lesson 6. — Temperature and Ventilation of Soils. 



1. Relation to plant growth. 



2. Relation to soil moisture. 



3. Relation to color. 



Exercise 6. — Factors influencing temperature of soils. 



Purpose: To impress upon the minds of the students the effects 

 of color, drainage, and slope of land upon the temperature of the 

 soil. 



Directions : Fill two boxes 12 inches square and 8 inches deep with 

 loam soil or the type of soil which prevails near the school, making 

 the surface smooth. Cover the surface of one with lampblack and 

 the other with powdered chalk or lime dust. Place both boxes in 

 the same horizontal positions in the sun. Insert thermometers about 

 one-half inch below the surface of each and take readings every hour 

 during the day until two or three hours after sunset. 



Fill two large flowerpots with the same kind of soil after the 

 drainage hole of one has been stopped up with paraffin. Saturate 

 each with equal amounts of water. Insert the bulb of a thermometer 

 an inch below the surface in each. Set in direct sunlight and take 

 readings twice each day for two or three days. 



Fill three boxes 12 inches square and 8 inches deep with loam soil 

 and set in line in the sunlight. Leave one level, tilt one 30° to the 

 north and the other 30° to the south. Using thermometers as before, 

 take readings every hour during a sunny day. 



Instead of using thermometers, seeds which are known to be viable 

 may be planted in the boxes and pots and the effects of the tempera- 

 tures noted upon the growth of the plants. It will be profitable also 

 to have each student take temperatures in the field of soils of differ- 

 ent colors, with different degrees of drainage and with different 

 slopes, in each case securing the same type of soil and securing all 

 conditions except the one tested as nearly equal as possible. 



Record and report: Each student should make a record in tabu- 

 lated form showing the temperature readings for the soils under the 

 73398°— Bull. 521—17 2 



