I 



The Soil and Soil Water 35 



The temperature of the soil plays a very important Tempera- 



f T i , i -i lure; effect 



part in the growing of crops. A light, dry soil warms O f water 

 up earlier in the spring than heavy, wet soil does. A 

 soil that contains too much water is always cold for two 

 reasons. It takes about live times as much heat to 

 warm water as it does to warm dry soil (Exp. 15), and 

 evaporation has a cooling effect, as we saw in Chapter 

 Two. If a field is sloping so a to be well drained and 

 the surface is kept loose and dry, the soil will be the 

 warmer. 



Experiments and Observations 



1. Examine a little garden soil with a hand lens, or preferably 

 with a microscope. 



2. Dig a hole through the soil to bedrock if you can, or exam- 

 ine the soil at the side of a road cut. Can you distinguish soil 

 and subsoil? 



* 3. Collect decomposed rock that has been softened or at least 

 stained by the action of the weather. Compare with an old break 

 in iron. 



4. Make several sieves about six inches square, with the sides 

 of wood and the bottoms of gauze wire. Let the different meshes 

 vary in diameter from the smallest mesh obtainable to one about a 

 quarter of an inch in diameter. After crushing all lumps in about 

 a quart of dry ga"rden soil, sift it thoroughly, using each sieve in 

 succession, beginning with the coarsest. Put the different sif tings 

 into separate glasses. Examine the samples carefully with the 

 naked eye and with a lens. t 



5. Put a handful of soil into a tall glass jar of water. Stir 

 thoroughly, and then watch the sorting action of water as settling 

 takes place. 



6. Collect in labeled bottles as many kinds of soil as possible. 

 Note on each label whether or not vegetable growth seemed good 

 in the locality from which the particular soil was taken. 



