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In a cultivated area, the soil has porosity of 45% and field capacity of 38%. For a particular crop, the root zone depth is 1.0 m, the permanent wilting point is 10% and the consumptive use is 15 mm/d. If the irrigation efficiency is 60%, what should be the frequency of irrigation such that the moisture content does not fall below 50% of the maximum available moisture?
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- 5d
- 6d
- 9d
- 15d
Correct Option: B
| Field capacity = | (W = r × v) | |
| Weight of soil |
| = | (Vv is used since water is in voids) | |
| rsoil × V |
| 0.38 = | × η |  | Porosity, η = |  | ||
| rsoil | V |
| ∴ | = | = | |||
| rw | 0.38 | 0.38 |
| Available moisture = | × (field capacity – wilting point) × depth | |
| rw |
| = | (0.38 – 0.1) × 1000 (d = 1 m = 1000 mm) = 331 mm | |
| 0.38 |
| Readily available moisture = | = 165 mm | |
| 2 |
| Number of days irrigated = | × 0.6 = ≈ 6 days | |
| 15 |
