HOW SOIL8 L08E WATER 105 



the soil with a great mass of decaying organic matter, 

 which xrvcs to hold much of the winter's rain, and 

 checks surface evaporation. Cultivated soils t hat have 



any tendency to wash or leach should never be left 

 bare to the action of the winter rains. 



Questions 



1. What are fertile soils? 2. If a soil fails to supply any 

 one of the essential plant foods what is it called? 3. How 

 does a soil become poor? 4. Name two important plant 

 foods often lacking In soils. 5. Why is it that deserts pro- 

 duce no plants? 6. How are the oases of deserts formed 

 and how may they become fertile? 7. If worn lands are left 

 uncultivated for any length of time what sort of crops 

 spring up? 8. How is the supply of water in soils renewed? 

 9. How is rain water held in soils? 10. How are plants 

 constantly supplied with water? 11. Why do soils covered 

 with growing plants or the litter of dead plants contain 

 more film moisture than bare fields? 12. Give an illustra- 

 tion of how plants protect soils from washing. 13. Why do 

 lands that have been cropped in tobacco or cotton suffer 

 from washing and leaching? 14. Which as a rule contain 

 more film moisture, lands left bare all winter or lands cov- 

 ered with vegetation? 



