Web Exam 7
Soil Science WEB Exam 7 Fall 2008 Dept. of Soil, Water and Climate
Directions 1. There is ONE BEST answer per question. 2.Place your answers on answer sheet, you only need to turn in the answers.
Name ___________________
1.________ 2._______ 3._________ 4._______ 5.______ 6._______ 7._________ 8._______
9.______ 10._______ 11. _________ 12.________ 13.______ 14.________ 15._________
Total _____
Soil Water-----------------------------------------------------------------------------------------------------------------------------
1) If a water molecule is held in a soil because it is close to a soil particle, the water is called __________.
a) capillary water
b) adhesion water
c) cohesion water
d) could be all of the above.
2) When water molecules are added to a moist soil _____________.
a) the molecules will be held by adjacent water molecules
b) the molecules are held by soil particles
c) the molecules move to the pore spaces and percolate from the soil.
d) the soil particles move apart to make room for the water molecules.
3. Wilt Point defines water held in the soil that is __________.
a) all available to the plant
b) some gravitational water and some plant available water
c) all at a potential that is to small for plants to absorb.
d) all adhesion water
4) Plant available water capacity (AWC) is ___________.
a) between -15 bar and -100 bar
b) between -1 bar and -15 bar
c) between -0.1 and -0.33
d) between -0.33 bar and -15 bar
5. The water held in a saturated soil will __?__
a) have a water potential of -1 bar
b) be variable depending on the size of the pore spaces.
c) be the same as the volume of pore space the soil has.
d) only exist in a soil if both small and large pores are present.
6. The mudball technique is used for estimating the field capacity of a soil. If the soil is normally at 20.5% water by weight at field capacity, what should the mudball weigh after you added 1 cc of water (1 gram). (Hint: mudball technique=(wt. water) ÷ (weight OD soil) x 100=% water)
a) 3.9 g b) 5.9 g c) 6.9 g d) 7.9 g
7. If a 405 g soil sample was collected from the field in a 400 ml container and after it was oven dried the sample weighed 352 grams. The percent water by volume at collection time would be?
a) 10.8%, b) 13.3%, c) 16.2 %, d) 20.4%
8. A soil has 13.5 % total available water holding capacity (AWC). Assume the soil is full of water and the plant roots are in the upper 30 inches of this soil. If the plants use 0.8 inches of water per week, how many weeks of water are available until the wilt point is reached?
a) 2 weeks b) 5 weeks c) 7 weeks d) 9 weeks
9. If the soil above is allowed to get very dry so that the % water by volume is 4 % , what would be the depth of wetting if it rains rains 1.55 inches or how deep will the rain penetrate into the soil? (Hint: Assume the rain fills the soil to field capacity before moving deeper into the soil and % water by vol at FC=16%).
a) 3 inches b) 9 inches c) 13 inches d) 16 inches
10. If a soil has 32% water by vol at field capacity and 10% water by vol at wilt point. What is the total potential Available water holding capacity for the upper 3 feet of this soil?
a) 2.9 inches b) 3.6 inches c) 4.3 inches d) 7.9 inches
11. The Ustic soil moisture regime is________________-
a) wetter than the udic regime
b) wetter in the summer than the aquic regime
c) wetter than the aridic regime
d) has a long dry spell in the spring
12. The common soil moisture regimes in
a) aquic, udic, ustic
b) ustic, aquic, udic
c) aquic, ustic, udic
d) udic, aquic, ustic
13. In the diagram if water enters this air dry
soil from only the bottom and top of the pipe that is in the middle of the soil, the water will
____________.
a) spread slowly at first from top and rapidly from the bottom, with equal spread from left and right..
b) spread rapidly from the bottom in concentric circles but very slowly from the top in circles of wetting front .
c) spread rapidly from the top but not from the bottom in concentric circles of wetting front
d) spread the same from the top and bottom in concentric circles of wetting front until some parts of the soil become saturated.
14. In the soil profile with the corn plant
growing in the loam topsoil, the sandy loam soil layer will _____. 
a) only be wetted by water that moves through the loam and clay loam and finally into the sandy loam from the surface.
b) rapidly become wetted once the clay loam is also wetted with water, since water would easily move into the large pores of the sandy loam. .
c) normally be dry since it has large pores compared to the small pores in the clay loam and loam.
d) be wetted in the lower part by capillary water rising from the water table, and wetted in the in the upper partafter the clay loam is saturated.
15. In the soil profile with the corn plant
growing in the topsoil, what is the total AWC in the upper 20 inches of soil. (Hint: the loam is 6 in., the clay loam is 6 in. and
the sandy loam is 8 inches thick)
Use this table.
Texture ...Available Water Capacity in Inches/foot of soil depth
Coarse Sands... 0.75
Fine Sands... 1.00
Loamy Sand... 1.20
Silt Loams... 2.50
Clay Loams... 2.00
Loam….2.5
a) 1.4 inches b) 2.9 inches c) 3.2 inches d) 4.4 inches
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