Chapter 4- Review Answers
Ans 1.Spaces between aggregates are likely to have a higher oxygen content, because the ped
interiors typically have small capillary-size pores that tend to hold more water, while the spaces
between peds are larger and less likely to be full of water
Ans 2. Structure could be maintained by avoiding heavy rototilling, annual additions of organic
matter, the use of organic mulches, and others.
Ans 3. Puddling does not change particle density, since that is based on the density of soil minerals,
and they have not changed. Texture is also unchanged, since puddling does not change the
proportions of sand, silt, and clay. Obviously, structure is degraded, which would cause an increase
in bulk density and a decrease in permeability.
Ans 4. Adding large amounts of organic matter should lower bulk density, because it should
improve structure. Because organic matter is of low density, increasing its percentage should also
lower soil density, though this effect is probably not as important.
Ans 5. Using the formula for porosity based on bulk density, the porosity of the grazed soil is 45%
while the porosity of the filter strip would be 60%. This certainly means much better structure
in the filter strip, higher organic matter content, and much improved water infiltration rates, which
is, of course, part of the point of a filter strip.
Ans 6. Loamy soils have the best balance of pore sizes. This would imply a good balance between
air-filled and water-filled spaces in the soil. Or, the soil will be well aerated with good water-holding
capacity.
Ans 7. You would prefer a light brown subsoil. The gray subsoil would suggest serious drainage
problems, which would be a challenge to homes with basements.
Ans 8. This soil would have a mere 0.1% clay. It would be a fine sand. From this description, we
would expect it to be excessively well drained (unless a high water table or some subsoil feature
retarded drainage), droughty, probably not strongly structured but friable because of the low clay
content.
Ans 9. According to Appendix 4:
a. moderately fine or fine
b. moderately coarse, medium
c. medium, moderately fine
d. moderately coarse through moderately fine
e. moderately coarse to medium
Ans 10. You will go to the sandier soil job sites first, because they will drain and dry down quicker,
and one should stay off wet soils. Sandy soils are less prone to compaction and crusting when wet.
Ans 11. Mixing a cubic yard of each will result in less than 2 cubic yards total volume because the
smaller particles will occupy large pores between the larger particles.
Ans 12. Eliminating 15 grams of coarse fragments make the remaining sample weigh 85 grams.
Dividing 32 grams of sand and 28 grams of silt by 85 yields 38 percent sand and 33 percent silt, and
29 percent clay which makes it a clay loam. Twenty-five percent of the original sample was clay,
and 15 percent was
coarse fragments. The percentage of clay in the texture is 100 percent minus that of silt and sand,
or 29 percent.
Ans 13. This is a procedure called field potting. The soil in the pot would weigh 1.2 grams per cubic
centimeter times 8,000 cubic centimeter, or 9,600 grams (9.6 kg). The definition of bulk density
specifies oven-dry soil. Because field soil will always be wetter than this, the real weight will be
greater.
Ans 14. The bulk density of this soil is 150 grams weight divided by a volume of 107, or 1.4 grams
per cubic centimeter. Porosity will be 100% – (1.4/2.65)x100 =47%
Ans 15. This is a simple rule for gardeners and landscapers in cold states: plants that are not fully
hardy should be mulched with something that will insulate the soil and protect the roots. This
means an organic mulch, which is much more protective than a rock chip or plastic mulch.
Ans 16. A rain garden is designed to intercept runoff and allow it to seep into the soil. If the
surrounding soils are clay, then the runoff may contain clay particles, which will filter in between
the designed soil particles and clog the large pores, retarding drainage. The rain garden would now
fill up and overflow during rain events, defeating its purpose.