Multiple choice

Direction: The moisture holding capacity of the soil in a 100 hectare farm is 18 cm/m. The field is to be irrigated when 50 percent of the available moisture in the root zone is depleted. The irrigation water is to be supplied by a pump working for 10 hours a day, and water application efficiency is 75%. Details of crops planned for cultivation are as follows:

   
Crop Root zone depth (m) Peak rate of moisture use
(mm/day)
X 1.0 5.0
Y 0.8 4.0

The capacity of irrigation system required to irrigate crop X in 36 hectares is

  1. 83 litres/sec

  2. 67 litres/sec

  3. 57 litres/sec

  4. 53 litres/sec
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Available moisture = 18 cm/m * 0.5 = 9 cm/m. For crop X (1.0m depth), depth = 9 cm = 90 mm. Peak rate = 5 mm/day. Interval = 90/5 = 18 days. Water required per interval = 90 mm * (36 hectares) = 0.09 m * 360,000 m^2 = 32,400 m^3. Daily requirement = 32,400 / 18 = 1,800 m^3/day. With 75% efficiency, required supply = 1,800 / 0.75 = 2,400 m^3/day. Pump works 10 hours = 36,000 seconds. Flow rate = 2,400 / 36,000 = 0.0666 m^3/s = 66.6 L/s.

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