AGRO 2244.  Sample Questions, Test 1, Physical properties of soils. 

NOTE TO STUDENT:

Please study the question contents!  DO NOT try to memorize questions and answers or you will get confused and not learn anything!  These only represent the type of information that you should have comprehended to be successful on this test. Do not expect these same questions to be on the test, they probably won’t be!  Some answers are denoted in red font.

 

____    A soil developed in the prairie ecosystem of the mid-west will have:

            A. a thin A horizon with a thick E horizon

            B. a thick, dark A horizon and no E horizon

            C. numerous B horizons that are acidic

            D. mostly clay textures

 

____    The soil solum is basically:

            A. the percent sand, silt and clay        B. the upper A and B horizons

            C. all unconsolidated material                        D. the mineral matter

 

____    The dominant water energy component in most field soils is:

            A. matric potential                              B. electrical potential

            C. osmotic potential                            D. gravity potential

 

____    Unsaturated flow of water in soils is related the most to:

            A. landscape position                          B. capillary pores

            C. macro-pores                                    D. organic matter and aggregation

 

____    Generally, which of the following soil textures has the ability to hold the most

            plant available water?

            A. silt loam                                          B. clay

            C. loamy sand                                     D. sandy loam

 

____    Soil aeration is mostly related with:

            A. oxygen levels                                 B. reduced iron levels

            C. nitrogen levels                                D.  moisture regime

 

____    As the bulk density of a soil increases, the percent pore space:

            A. decreases                                        B. increases

            C. stays the same regardless               D. shifts more to macro-pores

 

____    A soil horizon that has not weathered sufficiently to develop structure is given

            the letter designation:

            A. A                            B. B                             C. C                             D. E

 

____    Wind-blown, silt to silt loam size soil deposits are the parent material:

            A. residium                                         B. alluvium

            C. glacial till                                        D. loess

 

____    Soil differs from ‘dirt’ because it is:

            A. it is prettier and smells better         B. it is a growing medium for plants

            C. it is chemically more fertile            D. mostly mineral matter

 

Problems.  The calculations in the problem sets may or may not use these:

DB =            mass                    ,                      DP =      mass        ,

             bulk volume                                     soil solids

 

Ov = vol. water ,                     Om  =   mass  water  ,

         bulk vol. soil                                 dry wt soil

 

% pore space  =  (1  -  DB/DP)  100,              cm water  =  Ov  X  depth thickness (cm)

 

1 in  =  2.54 cm,          volume cylinder  =  π r2  L,  r = radius = diam./2,  L = length

 

1 g water = 1 cm3 ,  1 kg water = 1 m3,  density of water, lbs ft-3 (pcf)  =  62.4,   e = mc2

 

Problem set 1. 

Core samples, 3 in diam.  X  3 in length, of the surface horizon of two soils were obtained and the following data collected.  Complete the table where indicated.  SHOW ALL WORK FOR FULL CREDIT.  1 pt each.

 

wt. empty soil core  =  100 g

 

measurement                                                   soil A                           soil B

wet wt. core+soil                                            625 g                           638 g

 

oven-dry wt. core+soil                                    550 g                           525 g

 

% sand                                                                          76                                27

 

% silt                                                                 12                                 8

 

% clay                                                               12                                65

 

gravimetric moisture                                       _____                          _____

 

volumetric moisture                                        _____                          _____

 

bulk density (kg m-3)                                       _____                          _____

 

% pore space (assume DP = 2.7 kg m-3)          _____                          _____

 

USDA texture class                                        ________________    ________________   

 

a. Which soil, A or B, is the most dense?  one with greater bulk density

 

b. Which soil, A or B, will hold the most water at field saturation?  one with lower bulk density

 

Problem set 2

 

Given:

 

property                                   soil A               soil B

% sand                                                40                   12

 

% silt                                       40                   25

 

% clay                                     20                   63

 

color                                        10YR 3/2        5YR 5/4

 

bulk density (kg m-3)               1.1                   1.6

 

structure                                  granular           angular blocky

 

1. What soil holds the most water at 0 bar pressure? (1 pt)  one with lowest bulk density

 

2. What soil probably has the better overall soil tilth? (2 pts)  one with less clay

 

3. Which soil is more red in color? (1 pt)  5YR

 

4. Which soil is darker colored? (1 pt)  10YR 3/2

 

5. Which soil will probably have the greater shrink/swell potential from wetting/drying

    activity? (1 pt) one with greater % clay

 

6. What soil probably came from the A horizon? (1 pt) one with granular structure, most common in A horizons.

 

7. If you wanted to throw a clod of soil (a ‘dirt’ clod) at your sister and didn’t want

    to hurt her too bad (fearing the consequences), which soil would you probably get

    a clod from to chunk at your sister (then run like heck)?  (1 pt)

one with the lower bulk density.  Actually, I wouldn’t do that because she’d beat you up and your dad would too!

 

 

 

 

 

SHORT ANSWER, LISTING.  look up answers to these on your own.

1. List the five factors of soil formation.  (5 pts)

 

 

 

 

 

 

2. List three things that can affect soil bulk density.  (3 pts)

 

 

 

 

3. List three things that can influence soil aggregation.   (3 pts)

 

 

 

 

4. List five factors that can influence the absorption and transmission of heat in soils.

    (5 pts)

 

 

 

 

5. What properties of soil effect soil tilth?  (5 pts)