MOTHER EARTH 97 



4. Exhaustion of the soil 



Elements that are not likely to be exhausted 

 Elements that are constantly removed in considerable quantities 

 by crop plants : nitrogen ; phosphorus ; potash ; calcium 

 Effect on farming 



5. Use of fertilizers 



Purposes . Kinds 



To replace needed materials Quantities and costs 



To destroy injurious organisms 

 To alter the chemical state of the soil 



6. Organisms in the soil 



Injurious to plants 

 Helpful to plants 



7. How soil is made to yield more 



By selecting more prohfic varieties 



By selecting early-maturing varieties 



By covering against cold weather 



By artificial watering 



By more thorough tilling 



By systematic fertilizing of soil 



8. How more soil is made available 



By reclamation 



Swamp (drainage) ; desert (irrigation) 

 Limits in reclamation 



9. Waste of soil 



Rivers emptying into the sea (Relation to deforestation) 



Dissolved salt 

 Mechanically carried silt 

 10. Relation of soil to population 



The soil The people 



Quantity How they use the soil 



Quality How they use their knowledge 



How they deal with each other 



1, 



QUESTIONS 

 What kinds of fertilizers are produced in your part of the country? 



2. What kinds of fertilizers have to be imported into your region ? 



3. Why do farmers have to spend a larger part of their income for 

 fertilizers in some regions than they do in others ? 



