32 SOIL INGREDIENTS 



are produced when only an abundance of water is supplied. Ex- 

 periments in water culture, too, have proved that when nitrogen 

 is supplied to plants in the form of purely inorganic or mineral 

 nitrates, plants will thrive in the complete absence of humus." 



EXERCISES 



1. Secure samples of clay, sand, and loam. Expose them to the action of 

 the sun for an hour and note the temperature. 



2. If possible secure samples of humus and mix with each of the soils 

 previously mentioned. After moistening them thoroughly repeat the pre- 

 vious experiment and note temperatures as before. Explain the results. 



3. Secure dry samples of clay, sand, and soil and weigh each sample. 

 Add equal weights of water to each and after exposure to the action of the 

 sun for a day record the weights again. Note results and explain. 



4. Plant seed in each sample of soil and note the time required for germi- 

 nation. Explain the results. 



QUESTIONS 



1. Name some of the soil ingredients. 



2. Discuss sand and its value as a soil maker. 



3. Discuss clay and its properties. 



4. Of what does clay consist ? 



5. In what way is clay valuable to plant growth ? 



6. Compare sand and clay. 



7. Explain what is meant by loam. 



8. Discuss lime and its action on soils. 



9. Discuss humus and its' formation. 



10. What effect has humus on sandy soils ? 



11. Discuss the action of humus on clay soils. 



12. Should humus be used on wet lands ? Why? 



13. Where is the greatest amount of humus found ? Why ? 



14. What does Professor King say about the importance of humus as a 

 plant food ? 



REFERENCES 



The Soil, King. 



Soils, Burkett. 



The Soil of the Farm, Scott & Morton. 



Agriculture, Storer. 



