Question

The moisture content of the soil in the root zone of an agricultural crop at a certain stage is found to be $0.05$. The field capacity of the soil is $0.15$. The root zone depth is $1.2m$. The consumptive use of crops at this stage is $3mm/day$ and there is no precipitation during this period. Irrigation efficiency is $65\%$. It is intended to raise the moisture content to the field capacity in $8$ days through irrigation. The necessary depth of irrigation required is__

• A. 284 mm
• B. 314 mm
• C. 406 mm
• D. 456 mm

Answer 1

The correct option is B 314 mm

$\text{Depth of water required to raise the moisture content}\text{to the field capacity}=\frac{{\gamma }_d}{{\gamma }_w}(F_C-M_c)=1.5\times 1.2\times \times (0.15-0.05)$

$=0.18m$

Adding consumptive use @3.0 mm/day for 8 days

$=\text{Water required}=0.18+\frac{8\times 3}{1000}=0.204m$

Irrigation efficiency = 65%

$\therefore$ The required necessary depth of irrigation
$=\frac{0.204}{0.65}=0.31385m$

$=313.85mm\simeq 314mm$