6.8: Questions
- Page ID
- 44426
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)1. Explain why irrigation water does not have to be applied on exactly the same day that the AD is reached.
2. How do soil texture and plant rooting depth influence the frequency and amount of irrigation?
3. Explain why fdc is affected by ET.
4. What is the maximum desired depth of infiltration during an irrigation? Why?
5. Explain why infiltration often exceeds the maximum desired amount of infiltration. Does the uniformity of irrigation influence the amount of excessive irrigation?
6. Develop the water balance (AW) equivalent to Example 6.5.
7. Which do you prefer, the SWD approach or AW approach to the checkbook accounting method? Why?
8. Tensiometers where used in a field for estimating soil water depletion. The beginning position and the ending position of the irrigation system were sampled.
a. Determine the latest and the earliest dates for both positions given the following information:
| Tension | |||
|---|---|---|---|
| Layer (in) | Tensiometer Depth (in) | Beginning Position (cb) | Ending Position (cb) |
| 0–12 | 6 | 40 | 35 |
| 12–24 | 18 | 45 | 10 |
| 24–36 | 30 | 25 | 35 |
Root depth = 3 ft
Forecast ETc = 0.30 in/d
Soil type = fine sandy loam
AWC = 0.15 in/in
Effective irrigation depth = 1 in
Rainfall allowance = 0.5 in
fdc = 0.55
b. If the irrigation cycle time is 3 days, when would you recommend that the system be started and why?
9. The layers of a Hastings silt loam (Hc) are described below (taken from Soil Survey of Clay County).
| Depth (in) | Texture | AWC (in/in) | Bulk Density (g/cm3 ) |
|---|---|---|---|
| 0–10 | silt loam | 0.22–0.24 | 1.20–1.40 |
| 10–38 | silty clay | 0.11–0.20 | 1.30–1.40 |
| 38–60 | loam | 0.18–0.22 | 1.20–1.40 |
| silt loam |
If tomato roots are 48 inches deep, determine:
a. Total available water (TAW) in inches
b. AD (in inches) assuming that ETc = 0.24 in/d
c. MB (in inches) assuming that ETc = 0.24 in/d
d. The maximum interval between irrigation (TMAX) in days
10. Tensiometers are used in a loamy sand. Readings are taken as follows:
| Tension (cb) | |
|---|---|
| July 2 | 10 |
| July 4 | 12 |
| July 6 | 18 |
a. Using the graphical procedure (Figure 6.13), predict the date when irrigation will be needed.
b. If the root zone is 36 inches deep, at what depth should the tensiometer(s) be placed?
c. Discuss the pros and cons to this approach of scheduling.
11. Rework Example 6.6 given the following data:
| Day | Crop ET (in/d) | Pe (in) |
|---|---|---|
| Sunday | 0.25 | - |
| Monday | 0.35 | 0.70 |
| Tuesday | 0.15 | 0.10 |
| Wednesday | 0.30 | - |
| Thursday | 0.15 | - |
| Friday | 0.30 | - |
| Saturday | 0.20 | - |
12. If crop ET for the previous four days was 0.35, 0.20, 0.30, and 0.15 in/d and the effective depth of water applied per irrigation is 1.25 inches, how often should you irrigate? If a 0.75-inch rainfall occurs during this schedule, how many days can the system be left idle before it is restarted?
13. Site, crop, weather, and irrigation data are for a field area given below. Using the checkbook accounting approach, develop an irrigation schedule for July 1-14 for both the start position and the stop position. Do the ED and LD calculations on July 1 and July 8. For this 2-week period, tell us when the beginning and ending positions would be irrigated (keep in mind how fast the system can get to each point). Assume that on July 1, the system is in the start position.
Crop: Corn Irrigated area: 136 ac
Emergence date: 4/28 Gross depth applied: 1.0 in
Effective cover date: 7/10 Cycle time (Tc): 3 d
Date of maximum root depth: 8/1 ELQ: 85%
Maximum allowable depletion fdMAX: 0.50 Allowance for storing rainfall: 0.5 in
AWC: 0.18 in/in fr on 7/1 in the root zone:
System capacity: 850 gpm 0.70 (both positions)
Forecasted ET: 0.25 in/d fr below the root zone: 1.0
| Date | Crop ET (in/d) | Rain (in) | Root Dep |
|---|---|---|---|
| 7/1 | 0.31 | ||
| 2 | 0.18 | 0.15 | 30 |
| 3 | 0.21 | ||
| 4 | 0.20 | ||
| 5 | 0.25 | ||
| 6 | 0.36 | ||
| 7 | 0.22 | ||
| 8 | 0.25 | 33 | |
| 9 | 0.23 | ||
| 10 | 0.20 | 0.78 | |
| 11 | 0.26 | ||
| 12 | 0.22 | ||
| 13 | 0.35 | ||
| 14 | 0.23 |