2021_Integrative_Exam1_Worksheet_KEY
pdf
keyboard_arrow_up
School
Pennsylvania State University *
*We aren’t endorsed by this school
Course
101
Subject
Geology
Date
Jan 9, 2024
Type
Pages
3
Uploaded by CoachWaterPrairieDog22
KEY
for SOILS 101 Exam 1 practice problems and integrative problems – texture,
pores, soil genesis
à
Consider the following:
Soil 1: A soil with a thick A horizon that is a clay loam with high organic matter content
Soil 2: A soil with a thick A horizon that is a sandy loam with low organic matter content
Soil 3: A soil with a thin A horizon (loam + organic matter) underlaid by platy structures
à
Explain how these soils would perform for agriculture in the following regions.
Justify
with your knowledge of texture, pore sizes, and aggregates.
(a) A drought-ridden area
In a drought season, one would want the soil that retains water the best.
This would be
a soil with a greater amount of smaller pores, namely a finer-textured soil.
A high
organic matter content would also likely indicate the presence of aggregates, also
critical for retaining water.
As such, soil 1 would likely be good for this area.
(b)
In an area with plentiful rain year-round
Drainage is critical when there is plenty of rain.
Soil 2 would be a good choice.
As a
sandy soil, it would be documented by macropores.
Soil 1 could be an acceptable
choice as well, because with a high organic matter content it is likely to have many
aggregates, providing macropores between aggregates.
Soil 3 is fine as long as the
rain is not too heavy, because the platy structure would block drainage.
Loam will have
a distribution of pore sizes.
(c) In a commonly-flooded area with plants needing good aeration
Soil 3 may have drainage issues as the platy structures under the thin A horizon could
impede drainage.
Soil 2 and possibly soil 1 could also be suitable for the reasons
provided in (b).
à
Why are green sand beaches mainly found in areas with active volcanoes, and not in
other places?
Volcanoes indicate that igneous minerals are being generated (e.g. in emitted ash).
Igneous minerals weather easily.
In areas without active volcanoes, they will weather
away.
It is only in areas where igneous rock was recently generated that we can see
soils (including beach sands) that are made from this type of rock.
à
Iron oxides are resistant to weathering and are common in tropical rainforests.
Why?
In a hot, wet climate, the more easily-weathered minerals will have been washed away,
leaving behind the resistant minerals.
à
How does tilling (stirring up soil with a plow) change pore sizes in a soil?
Short term, tilling will increase macropores and mesopores and increase overall
porosity.
Long-term, due to destruction of aggregates, micro- and meso-pores will
decrease.
à
You notice in a baseball field area within a park that there are many patches with
puddles of water.
Why is this happening, and how could you address this problem as a
park manager?
Compression of the soil has converted most pores to being micropores that do not allow
for good drainage.
Erosion will likely have also resulted in loss of aggregates, again
resulting in the loss of macropores that would increase drainage.
If the puddling is happening in the outfield area, aerating the lawn (punching holes in the
grass) may be a good option for introduction of macropores.
Seeding the area with
specialized turf grasses would also help.
On the baseball diamond itself, regular raking
of the soil, as well as adding new soil with a coarser texture could help in ensuring more
macropores are present for drainage.
à
Farmer X has purchased land with a field taken over by an extremely aggressive
species of weeds.
Decades ago, the soil in the field was a dark, soft loam, but it has
become lighter and hardened over the years, commonly forming a crust.
He is aware
that prior management practices have degraded the soil, but still wants to use it as soon
as possible for a fast-growing, profitable crop.
He has the following tools at his disposal:
A chisel plow
A moldboard plow
Access to an effective herbicide (but it is expensive)
A sticky polymer for soil application
A tractor with narrow tires
A tractor with wide tires
(a) Explain what you think Farmer X should do with these tools and why.
Use your
knowledge of pores, organic matter, aggregates and tillage.
Tillage methods
I would suggest the use of the chisel plow.
This is because it will leave some surface
plant residues to guard against erosion and input organic matter, while still breaking up
the hardened soil to make it immediately available for planting.
The moldboard plow
would be too aggressive on an already compacted soil.
No-till agriculture is not a good option, as it would mean that the soil will not be available
for use potentially for years.
Also, to control weeds, one would have to use an
expensive herbicide as opposed to using a plow to mechanically break them up.
Tractor type
I would suggest using a tractor with wide tires.
This will decrease the pressure on the
soil and therefore limit compaction.
Sticky polymer
This could be useful for rapidly building aggregates to limit issues such as soil crusting.
(b) If the field were muddy, would you still recommend Farmer X do these things?
Why
or why not?
I would tell him to wait.
The soil would be more compressible when it is muddy and the
prospect for erosion would increase.
Plowing will compress soil much less when it is
dry.
à
Are highly-developed soils likely to be more or less fertile than undeveloped soils?
Explain and justify your answer, considering what you know about soil genesis,
weathering and leaching.
These may be less fertile, because more nutrients have been washed away (leached).
Igneous mineral content, which often can contain useful nutrients, would have long
been weathered away.
à
Why might forest soils in rainy areas need significant amounts of fertilizer?
Forest soils in rainy areas are likely to have had nutrients washed away from the A
horizon.
Forest soils are also more likely to have an E horizon, which is leached of
nutrients.
à
How does the introduction of dams in rivers change soils in the regions downstream?
Is this a problem for people farming such areas?
Explain.
Rivers carry alluvial parent materials rich in silt with easily weathered minerals (hence
good nutrient sources for crops).
Dams prevent the transport of this sediment to
downstream areas.
As such, those downstream soils are not receiving any new input
and can eventually be depleted.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help