TEXTURE AND STRUCTURE OF SOILS 45 



perhaps to lack of lime, or poor drainage, or they may 

 be characteristically deficient in phosphoric acid or even 

 in potash. Again a type is often indicative of the kind 

 of crops to which a soil is adapted, but as climate is a 

 large factor in determining the success of any crop, conclu- 

 sions of this nature are not of universal application. The 

 working qualities of a soil may usually be gauged with 

 some degree of certainty when the type is known. It is, 

 however, as a foundation for a further study of soils that 

 the survey is probably of greatest usefulness. 



QUESTIONS 



1. To what does the term " texture " refer when used with refer- 

 ence to soils ? 



2. Name the groups into which soils are divided by a mechanical 

 analysis. 



3. What characterizes the difference in mechanical composition 

 of soils adapted respectively to wheat, corn and potatoes ? 



4. What is meant by class as applied to soils ? 



5. In what class does soil belong that contains 20 percent clay 

 and 20 percent silt ? One that contains 40 percent clay and 30 per- 

 cent silt ? One that contains 25 percent clay and 35 percent silt ? 



6. How do soils containing a high percentage of clay or silt be- 

 have when wet ? How is their water capacity likely to compare 

 with that of a soil high in sand ? 



7. How do coarse and fine particles usually differ with respect 

 to their content of phosphoric acid, potash and lime ? 



8. What is meant by soil structure ? 



9. Distinguish between separate grain structure and granular 

 structure. Which permits of the greater amount of pore space ? 



10. Describe the relation of tilth to structure. 



11. Explain relation of structure to texture. 



12. Explain relation of structure to wetting and drying of soil. 



13. Explain relation of structure to freezing and thawing of soil. 



14. Explain relation of structure to organic matter. 



15. Explain relation of structure to roots and animals. 



16. How is structure affected by lime ? 



17. How is structure affected by tillage ? 



