42 A UNIT IN AGRICULTURE 



Ex. 26. Soil Temperature. 



Review Exercise 19. Which of the soils was warmest? What 

 coldest ? In the same jar of soil insert two thermometers, one to the 

 depth of 2 inches and one 6 inches. Do you notice any difference in 

 the temperature shown? Try this experiment out of doors and note 

 the temperature of the air as shown by the third thermometer sus- 

 pended a foot above the ground. Make three observations the same 

 day, one at 8:00 a. m., one at 2:00 p. m. and one at 6:00 p. m. Is 

 the surface of the soil warmer or colder than the air? Is this true 

 of all times of the day? If not, when? Is the average temperature 

 of the surface soil higher or lower than the average temperature of 

 the air? Which is more nearly uniform, the temperature of the air, 

 the surface soil or the soil at a depth of 6 inches? Do you know 

 whether each of your conclusions above will hold for different seasons 

 of the year? Should seeds be planted deeper or shallower in early 

 spring or late spring? Why? 



Ex. 27. Soil Drainage. 



Take two flower pots the same size and label them 1 and 2 re- 

 spectively. In No. 1 pour melted paraffin or wax to plug up the hole 

 so that no air can get through. In the bottom of No. 2 put about one 

 inch of fine pebbles or coarse sand. Nearly fill each pot with a 

 mixture of good soil and sand, three parts soil and one part sand. 

 Place in each pot a healthy growing plant of the same kind and size. 

 Sprinkle each with water till the soil is saturated and place the pots 

 in a sunny window. In each pot place a thermometer with a bulb at 

 a depth of two inches. Every two days note the temperature of the 

 soil and the condition of the plants in each pot. If each of these con- 

 ditions of soil and moisture were found in a field, which would be 

 more apt to be flooded in time of rain ? In which could the air pene- 

 trate more readily? In which would the temperature be higher? 

 Every two or three days apply equal quantities of water to each pot. 

 At the end of a month remove the plant, soil and all. In which pot 

 have the roots gone deeper? In which would they go deeper, the 

 drained or undrained soil? 



