Question

For an irrigated field having: Field capacity = 30%, Permanent wilting point = 10%, Permissible depletion of available moisture = 40%, Dry weight of soil = 14.70 kN/m${}^3$, Unit weight of water = 9.8 kN/m${}^3$ and Effective rainfall = 30 mm, what is the net irrigation requirement per meter depth of soil?

• A. 300 mm
• B. 150 mm
• C. 120 mm
• D. 90 mm

Answer 1

The correct option is D 90 mm

Total irrigation water requirement

$=0.4(0.3-0.1)\times \frac{14.7}{9.8}\times 1000$

$=0.4\times 0.2\times 1.5\times 1000$

= 120 mm

$\therefore$ Net irrigation requirement

= 120 - 30 = 90 mm