Ch 5 SoilWater PP2

QUIZ 6_Answers
1. Explain how a brush fire might lead to subsequent mudslides, as often occurs in California. (2)
Fire can significantly increase surface soil temperature
Volatilize soil organic matter
These org compounds move down through profile and condense on soil particles
Creates hydrophobic layer
Rain cannot infiltrate past layer, causes saturation of surface with water, increase
chance for mudslide.
2. What are the major components of soil water potential? (2)
gravitational, matric, osmostic
3. Describe the gravimetric method of measuring soil water content. (2)
weigh wet soil
dry the soil
reweigh the dry soil
subtract dry soil wt from wet soil wt to obtain mass of water
mass water content (Өm) = mass water/mass dry soil
4. The Waddell study used a tensiometer to measure the horizontal and vertical distribution of soil water pressures in
both the ridge-till and the no-till system. Figures 4 and 5 showed the difference in water potentials between 1)
right after a rain (Fig. 4) and 2) after seven days of drying (Fig. 5). The no-till plots showed level horizontal
distribution of soil water pressures in both figures (decreasing with depth), but the ridge-till figures indicated that
after seven days of drying water pressure was highest in the ridge and lowest in the furrows.
a. What was the direction of water movement in the ridge-till plot over that seven day period? (2)
away from ridge (water moves from high potential to low potential)
b. What potential implications does this have for soil temperature in the spring? (2)
If ridges are dryer than the surrounding soil, they will be able to warm more quickly.
This gives an advantage to ridge-till systems in northern climates while maintaining
overall high surface residue cover.
Soil Water continued…
Chapter 5
Chapter 5 Outline
I. Review
II. Journal Articles – General Concepts
III. Waddell Article
IV. Infiltration/Percolation
V. Field Capacity/Permanent Wilting %
Table 5.3
Stratified Soils
Fig 5.28
Michael J. Singer and Donald N. Munns
Soils: An Introduction, 6e
wetting front vs preferential flow
Michael J. Singer and Donald N. Munns
Soils: An Introduction, 6e
Fig 5.35
Classification of Soil Water
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