Question

Determine the field capacity, when the unit weight of water is 9.8 KN/m^3, and volume of water stored in unit area of soil is 28 m^3, the dry unit weight of soil is 18 KN/m^3, and the depth of root zone of the plant is 7 m.

(a) 2.178 m^2

(b) 2.135 m^2

(c) 2.125 m^2

(d) 2.25 m^2

I got this question during an online interview.

My question is from Water Requirements of Crops in section Water Requirements of Crops of Irrigation Engineering

Answer 1

Correct option is (a) 2.178 m^2

For explanation: We have, field capacity (F) = (weight of water retained in unit area of soil / weight of same volume of dry soil)

Weight of water retained in unit area of soil = γw x volume of water stored in unit area

= 9.8 x 28

= 274.4 KN

Weight of same volume of dry soil = γd x d (where, γw = unit weight of water, γd = dry unit weight of soil)

= 18 x 7

= 126 KN/m^2

Now field capacity (F) = (274.4 / 126)

= 2.178 m^2.