Question

What is the moisture depth available for evapotranspiration in the root zone of 1 m depth soil, if the dry weight of soil is 1.5 gm/cc, field capacity is 35% and the permanent wilting point is 15%?

1.

450 mm

2.

300 mm

3. 200 mm
4.

150 mm

Answer 1

Correct Answer - Option 2 :

300 mm

Concept: 

The depth of water stored (d_w) in the root zone is given by.

 \({d_w} = \frac{{{\gamma _d}}}{{{\gamma _w}}} \times d\left( {FC - PWP} \right)\)

where,

γd = dry unit weight of soil

γw = unit weight of water

d = depth of the root zone

PWP = Permanent wilting point

 FC - Field capacity

Calculation:

Given

 FC = 35 %, PWP = 15%

γd = 1.5 g/cc, γw = 1 g/cc

d = 1 m

The depth of water stored (dw) in the root zone

\(\therefore {d_w} = \frac{{1.5}}{{1}} \times 1 \times \left( {0.35 - 0.15} \right)\)

dw = 0.3 m = 300 mm