Question

If wheat requires about 75 mm of water after every 28 days, and the base period for wheat is 140 days, the value of delta for wheat is

• A. 2100 mm
• B. 75 mm
• C. 375 mm
• D. 750 mm

Hint:

The delta of a crop is a key parameter in irrigation design, representing the total water depth needed over the crop’s growth period. It’s calculated by multiplying the water depth per irrigation by the number of irrigations, based on the base period and irrigation interval.

Answer 1

The Correct Option is C

Step 1: Identify the given data.
Wheat requires 75 mm of water every 28 days, and the base period for wheat is 140 days. We need to find the delta (\( \Delta \)), which is the total depth of water required for the crop over its base period. The options are:
(1) 2100 mm
(2) 75 mm
(3) 375 mm
(4) 750 mm
Step 2: Recall the concept of delta in irrigation.
In irrigation engineering, the delta (\( \Delta \)) of a crop is the total depth of water (in mm or cm) required to grow the crop over its entire base period. It is calculated as:
\[ \Delta = (\text{Water required per irrigation}) \times (\text{Number of irrigations}) \] The base period (\( B \)) is the total duration of the crop’s growth (in days), and the irrigation interval is the time between consecutive irrigations (in days).
Step 3: Calculate the number of irrigations.
The base period is 140 days, and irrigation is required every 28 days. The number of irrigations (\( N \)) is:
\[ N = \frac{\text{Base period}}{\text{Irrigation interval}} = \frac{140}{28} = 5 \] This means there are 5 irrigations over the 140-day period (at days 0, 28, 56, 84, and 112, assuming the first irrigation is at the start).
Step 4: Calculate the delta.
Each irrigation provides 75 mm of water. With 5 irrigations:
\[ \Delta = 75 \, \text{mm} \times 5 = 375 \, \text{mm} \]
Step 5: Select the correct option.
The delta for wheat is 375 mm, which matches option (3).
\[ \boxed{375 \, \text{mm}} \]