The depth of root zone for a particular crop is 100 cm. If the dry unit weight of soil is 2.0 gm/cc of the field and its field capacity and permanent wilting point being 20% and 10% respectively, then the maximum storage capacity of irrigation water in cm will be

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Question

This question was previously asked in

BPSC AE Paper 6 (Civil) 14 Oct 2022 Official Paper

Answer 1

Concept:

For an irrigation land:

SC = Saturation capacity, FC = Field capacity, OMC = Optimum moisture content, PWP = Permanent welting point and UWP = Ultimate welting point

1. Equivalent depth of water held at field capacity (x) = S × d × Fc

2. Equivalent depth of water held at PWP (x’) = S × d × (PWP)

3. Available moisture/storage capacity of soil (y) = S × d × (Fc - PWP)

4. Readily available moisture content (dw) = S × d × (Fc - OMC)

Given:

Field capacity (F. C) = 20 % = 0.20

Permanent willing point (PWP) = 10 % = 0.10

Depth of the root zone (d) = 100 cm

Dry Unit weight of soil (γd) = 2.0 g/cc

Calculations:

The storage capacity

Hence, the storage capacity of the soil is 20 cm.