12 SOILS AND PLANT LIFE 



less familiar to us. Because it is so easily ignited, it is 

 much used in making matches. Iron, potassium, calcium 

 and magnesium are metals. These six elements combine 

 in many different ways in the soil, forming compounds 

 which, like those of nitrogen, are dissolved by the soil 

 water and carried along by it when it passes upward into 

 the plant. 



There are very few soils which are deficient in any of 

 the essential elements save nitrogen, phosphorus and potas- 

 sium. The great problem of maintaining a sufficient 

 supply of these three elements in the land so that agricul- 

 ture may be carried on perpetually remains one for the 

 consideration of all people who till the soil or expect to 

 continue to get from it an adequate food supply. The 

 strength of nations has always been drawn from the soil. 

 A system of permanent agriculture is therefore indispensa- 

 ble to the prosperity and happiness of our people. As a 

 fitting close to our first study of agriculture, we shall 

 make our last lesson one on maintaining the fertility of the 

 soil. 



QUESTIONS 



1. Define the term soil. 



2. Prom what three kingdoms do the materials for soils 

 come? 



3. Name three agents which have helped to break down rook. 

 Tell how each works. 



4. How can you separate soil into clay, sand and silt? 



5. Name three agents which have helped to mix soil. Tell 

 how each works. 



6. Define humus. How does a soil feel, when handled, 

 and how does it smell when it contains plenty of humus ? 



7. Compare the weight of a cupful of soil containing plenty 

 of humus with one lacking humus. 



8. Name the ten elements essential to plant growth and tell 

 how the plant gets each one. 



9. What part of the dry matter of plants is carbon? 



