Question

The following data pertains to healthy growth of a Crop:
1. Field capacity of soil = 32%
2. Permanent wilting point = 11%
3. Density of soil = $1500kg/m^3$
4. Effective depth of root zone = 75 cm
5. Daily consumptive use of water for the given crop = 12 mm
For healthy crop growth, moisture content must not fall down to 20% of the water holding capacity between the field capacity and the permanent wilting point, then the watering interval (in days) is

• A. 12
• B. 17
• C. 15
• D. 16

Answer 1

The correct option is C 15

Since, for healthy crop growth, moisture content should not fall below 20% of the water holding capacity between the FC and PWP.

Therefore, readily available moisture
= 80% of (FC- PWP)

$=\frac{80}{100}(0.32-0.11)=0.168or16.8\%$

So, if the readily available moisture is lost completely then we have to irrigate the crop.

Depth of water lost
$=\frac{\gamma }{{\gamma }_w}\times d\times \text{(Readily available moisture)}$

$=\frac{1500}{1000}\times 0.75\times 0.168$

$({\gamma }_w=1000kg/m^3$)

$=0.189m=189mm$

Daily consumptive use = 12 mm

$\therefore \text{Watering interval}=\frac{189}{12}=15.75days$

So, water should be applied after every 15 days because irrigation should be done before wilting commences.