Soils –205 General Soils

Study questions- Quiz 2

1) How does the structure of a water molecule influence its properties and behavior in soils?

2) A moist soil sample is collected in the field- the weight of the sample is 910 g and it has a volume of 500 cm³. After oven drying, the sample weighs 675 g. What is the gravimetric water content? The volumetric water content? What would the volumetric water content of this soil be at saturation?

3) What is meant by “soil water potential”? What are the three components that determine the total soil water potential (y_t)?

4) What is the importance of using soil water energy status to describe soil water?

5) Draw a graph showing the relationship between soil water potential and soil water content for a sand, loam, and clay.

6) Consider the following statement- water always moves downward in a soil. Do you agree or disagree with this statement? Why or why not? If water can flow upwards, what forces are involved?

7) Consider a soil profile in which a loamy sand E horizon overlies a sandy clay Bt horizon. If the soil is allowed to wet up as irrigation water is continually added at the surface, what will happen when the wetting front reaches the contact between these 2 horizons? Why?

8) Consider a soil profile in which a sandy clay Bt horizon overlies a loamy sand C horizon. If the soil is allowed to wet up as irrigation water is continually added at the surface, what will happen when the wetting front reaches the contact between these 2 horizons? Why?

9)

qv

Define the following terms: saturation, field capacity, permanent wilting point, and hydroscopic coefficient. What is the approximate soil water potential at each states defined above?

10) What is plant available water? How does it change with soil texture?

Soil water potential Y (kPa)

11) Compare and contrast saturated and unsaturated flow in soil. Be sure to address the driving forces and approximate water potentials over which each occur.

12) In the following diagram, will water flow from soil A to B, or soil B to A?

Soil A Soil B

qv = 14% qv = 20%

13) How does hydraulic conductivity (K) change with water content in a sand? In a clay?

14) What are the possible fates of water that has infiltrated the soil?

15) Approximately what fraction of the earth’s water is actively cycling? What implications does this have on importance of good soil management?

16) What does the term evapotranspiration mean. What is PET?

17) What factors influence evaporation?

18) How are soil aeration, water content and microbial activity related?

19) What are three ways of characterizing soil aeration?

20) What is the oxidation-reduction or redox potential?

21) What are the functions of wetlands?

22) What are three features that scientists look for when defining a wetland?

23) Is every seasonally saturated soil a Hydric soil? Why are why not?

24) What are three features of hydric soils?

25) What three factors (in terms of energy balance) that influence changes in soil temperature?

26) If all other factors are equal, do wet soils or dry soils warm up first in the spring? Why?

27) How do mulches influence soil temperature?

28) Describe how fire affects soil:

a. chemical properties

b. physical properties

c. biological properties

29) What is sheet, rill, and gully erosion? How are they related?

30) What are the components of the Universal Soil Loss Equation and how do they affect water erosion?

A = RKLSCP