The moisture content of soil in the root zone of an agricultural crop ...
Solution:
Given parameters:
- Moisture content of soil in the root zone = 0.05
- Field capacity of the soil = 0.15
- Root zone depth = 1.1 m
- Consumptive use of crop = 2.5 mm/day
- Precipitation = 0 mm/day
- Irrigation efficiency = 65%
- Time period for raising moisture content to field capacity = 8 days
Calculations:
1. Depletion of soil moisture due to consumptive use:
The depletion of soil moisture due to the consumptive use of the crop can be calculated as:
Depletion depth = Consumptive use x Time period
= 2.5 mm/day x 8 days
= 20 mm
2. Water required to raise moisture content to field capacity:
The water required to raise the moisture content of the soil from 0.05 to 0.15 can be calculated as:
Water required = (Field capacity - Moisture content) x Root zone depth
= (0.15 - 0.05) x 1.1 m
= 0.11 m
3. Total water required for irrigation:
The total water required for irrigation can be calculated as:
Total water required = Water required / Irrigation efficiency
= 0.11 m / 0.65
= 0.169 m
Therefore, the necessary depth of irrigation is 0.169 m.
Explanation:
- Soil moisture content: The soil moisture content is an important parameter that determines the availability of water to the crops. In this problem, the initial moisture content of the soil is given as 0.05.
- Field capacity: The field capacity of the soil is the maximum amount of water that the soil can hold against the force of gravity. In this problem, the field capacity of the soil is 0.15.
- Root zone depth: The root zone depth is the depth of soil in which the crop roots are present. In this problem, the root zone depth is given as 1.1 m.
- Consumptive use: The consumptive use of the crop is the amount of water that is used by the crop through transpiration and evaporation. In this problem, the consumptive use of the crop is given as 2.5 mm/day.
- Precipitation: The precipitation is the amount of water that is received from rainfall. In this problem, there is no precipitation during the time period for irrigation.
- Irrigation efficiency: The irrigation efficiency is the ratio of the amount of water that is beneficially used by the crop to the total amount of water applied. In this problem, the irrigation efficiency is given as 65%.
- Time period: The time period for raising the moisture content of the soil to the field capacity is given as 8 days.
- Depletion of soil moisture: The depletion of soil moisture due to the consumptive use of the crop is calculated by multiplying the consumptive use with the time period.
- Water required: The water required to raise the moisture content of the soil from 0.05 to 0.15 is calculated by multiplying the difference between the field capacity and the moisture content with the root zone depth.
- Total water required: The total water required for irrigation is calculated by dividing the water required by the irrigation efficiency.
The moisture content of soil in the root zone of an agricultural crop ...
Depth of water required for root zone
dω = S.d [Fc – ω]
Assume mass specific gravity, S = 1.40
dω = 1.4 × 1.1 [0.15 – 0.05]
= 0.154 m = 154 mm
Total consumptive use of water for 8 days
= 8 × Cu = 8 × 2.5 = 20 mm
Total depth of water to be stored in root zone = 154 + 20 = 174 mm
η = 65%
Total depth of water to be supplied =
174
η
=
174
= 267.7 mm ≈ 285 mm