CHAPTER XXIII 

 PHYSICAL STRUCTURE AND FERTILITY OF THE SOIL 



287. Questions for Discussion. 1. What kinds of soils in your com- 

 munity are considered the most valuable? For what purposes? Is 

 most of the soil in your community of this best type ? 2. What are the 

 different kinds of soil recognized in your state ? To what extent does 

 the value of farm lands vary according to the predominant kind of 

 soil? 3. Are the drained lowlands more fertile than the highlands? 

 Whv? 4. In what ways do plants and animals contribute to the de- 

 velopment of soils in uncultivated areas? Can you prove that plants 

 help to form soils? 5. Mow do earthworms contribute to enrichment of 

 soils? 6. Do you know any reason for cultivating the soil other than 

 killing weeds? 7. What effect would a heavy growth of weeds have on 

 the underground water supply available for crops? 8. In loose, sandy 

 soils, near rivers or lakes, to what level is it necessary to dig to -secure 

 a supply of water? Does this have anything to do with cultivation of 

 the soil ? 9. Which is heavier, a cubic foot of dry sand or a cubic foot 

 of dry clay? 10. What causes a desert? Are all deserts sandy? 



288. Kinds of soil. If we examine a handful of the soil 

 from near a lake shore we may find it chiefly composed of 

 sand. Sometimes this sand is coarse or gritty and sometimes 

 it is almost as fine and smooth as flour. Near the water's 

 edge quite coarse sand may usually be found. Back from the 

 lake, where plants are growing abundantly, the sand is dis- 

 colored and contains the substances resulting from decay of 

 plant and animal bodies. Where decayed organic matter is 

 abundant the soil is called loam. In some streams of water 

 along the riffles small stones are found in large numbers, and 

 more or less sand is mixed with them. This material is 

 gravel, and a soil in which such material predominates is 

 gravelly soil. Often by digging only a little way down we 

 find a soil which is composed of very fine and compact 



