Midterm #1 questions
APBI 200, Midterm Exam No.1, February 4, 2019
1.Bob got a summer job with a local forestry company. His boss has asked him to assess a forest plot. The surface of the mineral soil has a clay loam texture and a bulk density of 1.15 g/cm3. The plot was harvested, and after harvesting the soil had a bulk density of 1.60 g/cm3.
a)What was the soil porosity (f) in this plot before and after timber harvesting?
Show all steps of your calculation, including the units!
b)Would you expect that most of this change in porosity after harvesting was in the macropores or in the micropores? Briefly explain.
c)How would this compaction induced change in the pore size distribution (as explained in your answer to question 1b) affect water infiltration (i.e., water entering the soil). Briefly explain.
[6 points]
2.Define the paired terms shown below. Identify important distinctions between the paired terms. Consider how they differently affect what goes on in the soil and/or how plants grow on that soil. a)soil texture and soil structure b)permanent wilting point and field capacity [12 points]
3.Water retention curves A and B represent two soils with different texture and structure. Soil A Soil B
a)Identify and define the property that is indicated by the arrows on the two graphs. Briefly describe how this property differs between soil A and B. b)Identify the most likely texture and structure for these two soils. Briefly describe your reason(s). c)Explain how and why these two soils differ in terms of water retention as the matric potential decreases from 0 to -150 m. [7 points]
Multiple choice [1 point each]
4.The bulk density of a soil is the: a)mass of solids / volume of solids b)mass of solids / total soil volume c)volume of pores / total soil volume d)1 – (volume of pores / total soil volume)
5.Heat transfer in soils is largely due to: a)conduction b)convection c)radiation
6.Thermal admittance indicates: a)how fast a soil will heat up or cool down at depth b)how rapid a soil will heat up or cool down at the surface c)the ability of a soil to hold (or store) heat
7.Water moves in a soil: a)due to differences in gravitational potential b)due to a difference in total potential energy c)as runoff d)due to tortuosity
8.Why do phyllosilicate clay minerals in soils have a net negative charge: a)substitution of Si4+ for K+ in the octahedral sheet b)substitution of Fe2+ (or Mg2+) for Al3+ in the tetrahedral sheet c)substitution of Fe2+ (or Mg2+) for Al3+ in the octahedral sheet d)because they are often found in various soil types
Multiple answer [1 point each]
9.Soil texture includes: a)% sand b)% organic matter c)% silt d)% soil water e)% clay
10.The rate of water flow (flux density) in a soil depends on: a)the density of water b)water content c)particle density d)pore size
11.The definition of a soil includes: a)air and water b)living organisms c)mineral and organic particles d)sediment e)a static natural body f)medium for plant growth
12.A soil with a high specific surface area has: a)a low soil water retention b)a high soil water retention c)a fine texture d)a coarse texture e)rapid soil water drainage
13.Soil physical weathering: a)results in a change in chemical structure b)decreases the size of particles c)incudes the process of hydrolysis d)includes the process of abrasion e)decreases specific surface area
Fill in the blank [1 point each]
14.The fine earth fraction of the soil (sand, silt and clay) have diameter smaller than ________. (give the value and units)
15.Montmorillonite is a ________________ clay mineral.
16.Soil aggregates are formed by _______________ + _______________ .
17.In a well vented, unsaturated soil, with low solutes, the total soil water potential is due to __________ potential + ___________ potential.
18.The five factors of soil formation are: _______, _______, _______, _______, and ______ .