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 
