How to Determine the Frequency of Irrigation
Mathematical Problem
The following data are given to determine the frequency of irrigation
- Field capacity of soil = 45 %
- Permanent wilting point = 19 %
- Density of soil = 1.5 g/cm3
- Depth of root zone = 65 cm
- Daily consumptive use of water = 18 mm
Solution:
Available moisture = Field Capacity – Permanent wilting point = 45 – 19 = 26
Let readily available moisture = is 75 % of the available moisture,
So, readily available moisture is = 26 × 0.75 = 19.5 %
Optimum moisture content = 45 – 19.5 = 25.5 %
Now, by applying irrigation water the moisture content is to be raised from 25.5 % to 45 %.
Calculate the depth of water to be applied in each watering, by using the following equation:
[latex]D_{w} = \frac{W_{s}\times d}{W_{w}}\times [F_{c}-M_{0}][/latex]
Where,
- Ws = Unit Weight of soil or density of soil = 1.5 g/cm3
- Ww = Density of water = 1g/cm3
- d = Depth of root zone = 65 cm
- Fc = Field capacity = 45 %
- M0 = Optimum moisture content = 25.5 %
After putting the all value,
[latex]D_{w} = \frac{1.5\times 65}{1}\times\left [ 0.45 – 0.255 \right ][/latex]
[latex]Or, D_{w} = 97.5 \times 0.195 = 19.01 [/latex] cm
Now, we can calculate the frequency of irrigation by using the following equation
[latex]f_{w} = \frac{D_{w}}{C_{u}}[/latex]
Where,
- fw = Frequency of watering or frequency of irrigation
- Cu = Daily consumptive use of water =
- Dw = Depth of water to be applied in each watering
After putting all values, the frequency of irrigation
[latex]f_{w} = \frac{19.01}{1.8} = 10.56 = 11 days (say)[/latex]
Read Also:
Find the Intensity of Rainfall