2.12: Questions
- Page ID
- 44347
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)1. Would a fine-textured soil have a higher or lower available water capacity than a coarsetextured soil? How would the bulk densities compare? Explain why the differences, if any, occur.
2. Describe total soil water potential and its components. Why is matric potential important in irrigation management?
3. Will water infiltrate into the soil even if the root zone is at field capacity? If so, where will the water be stored? Explain.
4. Repeat Question 3 for a saturated soil.
5. Show mathematically how Equation 2.13 is derived from Equation 2.12.
6. The use of wetting agents has often been suggested to enhance infiltration. Wetting agents act by reducing the surface tension of the liquid. What effect does this have on capillary forces and infiltration? Explain.
7. An irrigation of 2.5 in of infiltration is followed by 1 in of rainfall infiltration. If a clay loam soil had a 50% depletion of the available water (fd = 0.5) prior to the water application and the root zone depth is 30 in, how much water would deep percolate?
8. If the average count ratio for neutron scattering measurements was 1.0, how much water needs to be infiltrated to bring a silt loam soil to field capacity?
9. A soil to be irrigated has two layers: the top layer is a silt loam 12 in deep and the other is a silty clay with a thickness of 3 ft. If both layers were at the permanent wilting point, how much water could be applied without water draining below the first layer? Second layer?
10. If you install a granular matrix sensor into the silt loam soil depicted in Figure 2.6 and the reading was 35 cb, what would be the volumetric water content of this soil? If the bulk density of the soil was 1.35 g/cm3 , what would be the mass water content?
11. If the average count ratio from a series of measurements with the neutron probe whose calibration is shown in Figure 2.16 on a golf course was 0.5 before irrigating and 0.9 after irrigating, how much water was added to a soil profile 1 ft deep?
12. A soil sample was taken just prior to irrigation and weighed wet then dried and reweighed.
The following data were obtained:
Wet mass = 240 g
Dry mass = 200 g
The soil has the following characteristics:
θfc = 0.30 cm3 /cm3
θwp = 0.10 cm3 /cm3
ρb = 1.25 g/cm3
Determine the following:
θm = mass water content
θv = volumetric water content
fr = fraction of available water remaining
fd = fraction of available water depleted
13. Tensiometers are placed in a fine sandy loam soil at depths of 6, 18, and 30 in.
The following readings were taken:
| Depth (ft) | Tensiometer Reading (cb) |
|---|---|
| 6 | 30 |
| 18 | 70 |
| 30 | 50 |
Use Figure 2.6 to help answer the following questions. Assume each tensiometer reading represents 1 ft of soil.
a. Determine the available soil water remaining at each depth (in/ft).
b. Determine the total available soil water remaining, in inches, in the 3-ft profile.
c. What is the fraction depleted in each layer?
d. How much water would have to be applied to bring the soil water level to field capacity to a depth of 3 ft?
14. Answer the following:
a. Using the soil water release curves shown in Figure 2.6, determine the expected soil moisture tensions at fd = 0.3 and fd = 0.6 for the silt loam soil.
b. Repeat (a) for the fine sand.
c. Would a tensiometer work properly for the four cases in (a) and (b)? Explain your answer.
15. The feel and appearance method was used to estimate the soil water in the following layers:
| Depth (ft) | fr |
|---|---|
| 0-1 | 0.55 |
| 1-2 | 0.65 |
| 2-3 | 0.60 |
| 3-4 | 0.80 |
| 4-5 | 0.80 |
| 5-6 | 0.80 |
| 6-7 | 0.80 |
a. If the volumetric water content at field capacity and wilting point is 0.35 and 0.13, respectively, how deep would 4.2 in of infiltrated water penetrate into the soil profile? Give your answer in inches.
b. If the root zone depth is 30 in, how many inches of water would percolate below the root zone?