This section describes how to determine the performance of basin/furrow irrigation. It is assumed that the net irrigation water need of the crop is known (i.e. the net irrigation depth). This is compared with what happens during the actual irrigation practice. The field application efficiency thus obtained is a good measure for the evaluation of the performance.
Figure 81 Place wooden posts at 5 a intervals
Equipment needed
- Measuring tape (30 m)
- Infiltrometer
- Wooden posts or lathes
- Stopwatch or clock
- Data sheet
Method
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Step 1: |
Identify a typical basin or furrow, which can be considered representative of the local situation in terms of size, soil type and crop. Measure the basin size or furrow length with the tape. Record the site data on the data sheet: | ||
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Example: | ||
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Date of test: 4 December 1987 |
Basin size: 24 (m) x 15 (m) - 360 (m2) | |
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Crop: Groundnuts |
Required net irrigation depth: 45 mm | |
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Step 2: |
Place wooden posts at 5 to 10 m intervals as shown in Figure 81. Record position of the posts on the data sheet (column 2). | ||
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Step 3: |
Carry out several infiltration tests (see Annex 3) and make an (average) infiltration curve. In this example, the curve of Annex 3 (Figure 76) is used. | ||
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Step 4: |
Now the irrigation starts. Use the same stream size and the same irrigation time as the irrigator normally uses. Record the time it takes for the water front to reach each wooden post (1 to 6). This is called the advance time: column 3. | ||
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Step 5: |
Record the time it takes the water to infiltrate at each wooden post (1 to 6). This is called recession time: column 4. | ||
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Step 6: |
Calculate the contact time at each of the wooden posts. The contact time is the difference between the advance and recession time: column 5. | ||
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Step 7: |
Calculate at each of the wooden posts the amount of water applied, using the infiltration curve: in this case Figure 76: column 6. All data are recorded on the data sheet as indicated in the example below. | ||
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Step 8: |
Determine the field application efficiency. | ||
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The field application efficiency is the fraction of the applied water that is used by the crop. Provided there are no runoff losses, the field application efficiency (%) is the required irrigation depth (mm), divided by the average applied irrigation depth (mm), multiplied by 100%. | ||
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Or: | ||
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The average irrigation depth applied (column 6) is: | ||
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(65 + 63 + 61 + 60 + 56 + 46):6 = 59 mm | |
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The required net irrigation depth is 45 mm. | ||
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Thus the field application efficiency (%) = 45/59 x 100% = 76% | ||
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It means that the (average) deep percolation losses are 59 - 45 = 14 mm. This is shown in Figure 82. | ||
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1 |
2 |
3 |
4 |
5 |
6 |
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Post No. |
Distance from field channel |
Advance time |
Recession time |
Contact time |
Water applied |
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clock reading |
time elapsed since start |
clock reading |
time elapsed since start |
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m |
hr |
min |
min |
hr |
min |
min |
min |
mm |
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1 |
0 |
11 |
00 |
0 |
11 |
50 |
50 |
50 |
65 |
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2 |
5 |
11 |
04 |
4 |
11 |
50 |
50 |
46 |
63 |
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3 |
10 |
11 |
08 |
8 |
11 |
50 |
50 |
42 |
61 |
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4 |
15 |
11 |
11 |
11 |
11 |
51 |
51 |
40 |
60 |
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5 |
20 |
11 |
20 |
20 |
11 |
52 |
52 |
32 |
56 |
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6 |
24 |
11 |
30 |
30 |
11 |
54 |
54 |
24 |
46 |
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Average |
59 mm |
Figure 82 Deep percolation losses
DATA SHEET IRRIGATION PERFORMANCE
