GATE Civil Engineering (CE) 2020 Shift 2 Solved Paper

Question : 46 of 65

Marks: +1, -0

Crops are grown in a field having soil, which has field capacity of

30 \%

and permanent wilting point of

13 \%

. The effective depth of root zone is

80 {cm}

. Irrigation water is supplied when the average soil moisture drops to

20 \%

. Consider density of the soil as

1500 {kg} \/ {m}^{3}

and density of water as

1000 {kg} \/ {m}^{3}

. If the daily consumptive use of water for the crops is

2 {mm}

, the frequency of irrigating the crops (in days), is

Solution:

Given: Final capacity

=30 \%

Permanent wilting point

=13 \%

Depth of root zone

=80 {cm}

Density of soal

=1500 {kg} {/} {m}^{3}

Density of water

=1000 {kg} {/} {m}^{3}

Consumptive use

= {Cu}=2 {mm}

{d}=\;{δ × {d}_{ {rz}} ×( {FC}- {PWP}) × {D}}/{δ_{ {w}}}

{d}=\;{1500 × 0.8 ×(0.3-0.13) × 0.8}/{1000}=163.2 {mm}

F_{01}=\;{d}/{C u}=\;{164}/{2}=82

days

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