1. Concept Explanation (Exam-Focused)
Crop Water Requirement (CWR)
Crop Water Requirement is the total quantity of water required by a crop for its full growth period.
It includes:
Evapotranspiration
Water for land preparation
Losses during application
Mathematically:
CWR = ET + Losses
Duty (D)
Duty is defined as:
Area of land (in hectares) that can be irrigated by 1 cumec of water flowing continuously during the crop period.
Unit: hectare/cumec (ha/cumec)
High duty → less water used
Low duty → more water used
Delta (Δ)
Delta is the total depth of water required by a crop during its entire base period.
Unit: meters or cm
2. Important Formulas (Most Repeated)
Basic Relation Between Duty and Delta
Δ=8.64×BD\Delta = \frac{8.64 \times B}{D}Δ=D8.64×B
Where:
Δ = Delta (m)
B = Base period (days)
D = Duty (ha/cumec)
🔥 Most repeated in exams
Duty Formula
D=8.64×BΔD = \frac{8.64 \times B}{\Delta}D=Δ8.64×B
Water Required
Water=Area×DeltaWater = Area \times DeltaWater=Area×Delta
Units:
Area in hectares
Delta in meters
Water in hectare-meter
3. Short Notes / One-Liners
• Delta is independent of time, duty depends on time.
• Higher delta → lower duty.
• Rice has high delta, wheat has low delta.
• Delta includes all field losses.
• Base period = time between first watering and last watering.
• 1 ha-m = 10,000 m³ of water.
4. PYQ Patterns (SSC JE / RRB JE)
Common Trends:
Direct numerical from Δ = 8.64B/D
Conversion of units (cm ↔ m)
Compare crops based on duty/delta
Conceptual MCQs on definitions
Typical Traps:
• Forgetting 8.64 constant
• Using delta in cm instead of meters
• Confusing base period with crop period
• Mixing up duty & discharge units
5. Solved Examples
Example 1 (Numerical)
Duty of a crop is 1200 ha/cumec and base period is 100 days. Find delta.
Δ=8.64×1001200=0.72 m\Delta = \frac{8.64 \times 100}{1200} = 0.72 \text{ m}Δ=12008.64×100=0.72 m
Example 2 (Conceptual)
Which crop needs more water – rice or wheat?
Rice, because it has higher delta and lower duty.
6. MCQs (Exam Level – 50)
Q1. Duty is expressed in:
A) m³/s
B) ha/cumec
C) m
D) cm
✅ Answer: B
📝 Explanation: Duty = Area irrigated per unit discharge.
Q2. Delta of a crop depends on:
A) Soil only
B) Climate only
C) Crop type and base period
D) Canal slope
✅ Answer: C
Q3. If delta increases, duty will:
A) Increase
B) Decrease
C) Remain same
D) Become zero
✅ Answer: B
Q4. Unit of delta is:
A) m³/s
B) ha
C) m
D) ha/cumec
✅ Answer: C
Q5. The constant 8.64 comes from:
A) Area conversion
B) Time conversion
C) Velocity relation
D) Empirical value
✅ Answer: B
📝 Explanation: 1 day = 86400 seconds.
Q6. The base period of a crop is:
A) Time between sowing and harvesting
B) Time between first watering and last watering
C) Time between two irrigations
D) Total crop life
✅ Answer: B
📝 Explanation: Base period is the irrigation period only.
Q7. Which has maximum delta?
A) Wheat
B) Sugarcane
C) Rice
D) Barley
✅ Answer: C
Q8. If duty is 800 ha/cumec and base period is 120 days, delta is:
A) 0.96 m
B) 1.2 m
C) 1.08 m
D) 1.3 m
Δ=8.64×120800=1.296≈1.3\Delta = \frac{8.64 \times 120}{800} = 1.296 \approx 1.3Δ=8008.64×120=1.296≈1.3
✅ Answer: D
Q9. High duty indicates:
A) More water requirement
B) Less water requirement
C) Poor soil
D) Heavy rainfall
✅ Answer: B
Q10. Which of the following is independent of time?
A) Duty
B) Delta
C) Base period
D) Discharge
✅ Answer: B
Q11. Unit of crop water requirement is:
A) m³/s
B) m
C) ha-m
D) cm/day
✅ Answer: C
Q12. If delta is 0.8 m and base period is 80 days, duty is:
D=8.64×800.8=864D = \frac{8.64 \times 80}{0.8} = 864D=0.88.64×80=864
A) 800
B) 850
C) 864
D) 900
✅ Answer: C
Q13. Which crop requires maximum water?
A) Wheat
B) Rice
C) Pulses
D) Barley
✅ Answer: B
Q14. Delta mainly depends on:
A) Discharge
B) Soil type
C) Crop type
D) Canal length
✅ Answer: C
Q15. If duty is doubled, delta becomes:
A) Doubled
B) Halved
C) Same
D) Zero
✅ Answer: B
Q16. CWR does not include:
A) Evaporation
B) Transpiration
C) Runoff losses
D) Effective rainfall
✅ Answer: C
Q17. The relationship between duty and delta is:
A) Direct
B) Inverse
C) Linear
D) Exponential
✅ Answer: B
Q18. Which one is correct?
A) High delta → High duty
B) Low delta → Low duty
C) High delta → Low duty
D) Duty independent of delta
✅ Answer: C
Q19. Delta is expressed in:
A) cm/day
B) m³/s
C) m
D) ha
✅ Answer: C
Q20. If base period is zero, delta will be:
A) Infinite
B) Zero
C) Maximum
D) Negative
✅ Answer: B
Q21. 1 hectare-meter equals:
A) 1000 m³
B) 5000 m³
C) 10,000 m³
D) 8640 m³
✅ Answer: C
Q22. Which factor increases duty?
A) More losses
B) Efficient irrigation
C) Sandy soil
D) Long base period
✅ Answer: B
Q23. Delta is maximum for:
A) Short duration crops
B) Long duration crops
C) Rainfed crops
D) Rabi crops
✅ Answer: B
Q24. If delta is 1 m for 200 ha area, water required is:
A) 100 ha-m
B) 200 ha-m
C) 300 ha-m
D) 400 ha-m
✅ Answer: B
Q25. Which is a trap statement?
A) Delta depends on crop
B) Duty depends on time
C) Delta depends on time
D) Duty depends on delta
✅ Answer: C
Q26. For same crop, if soil is sandy, duty will be:
A) Increase
B) Decrease
C) Same
D) Zero
✅ Answer: B
Q27. The term 8.64 is used to convert:
A) hours to seconds
B) days to seconds
C) m³ to liters
D) hectares to m²
✅ Answer: B
Q28. Which crop has lowest duty?
A) Rice
B) Wheat
C) Pulses
D) Barley
✅ Answer: A
Q29. Base period is expressed in:
A) m
B) sec
C) days
D) ha
✅ Answer: C
Q30. If duty is infinite, delta will be:
A) Zero
B) Maximum
C) Negative
D) Infinite
✅ Answer: A
Q31. Duty is maximum for:
A) Paddy
B) Sugarcane
C) Wheat
D) Cotton
✅ Answer: C
Q32. Which one is not part of CWR?
A) Consumptive use
B) Percolation loss
C) Runoff
D) Land preparation
✅ Answer: C
Q33. Delta is minimum for:
A) Rice
B) Sugarcane
C) Wheat
D) Barley
✅ Answer: D
Q34. Duty mainly depends on:
A) Crop
B) Climate
C) Irrigation method
D) All of the above
✅ Answer: D
Q35. The crop period is:
A) Base period
B) Total growth period
C) Irrigation period
D) Sowing period
✅ Answer: B
Q36. For a given delta, increasing base period will:
A) Increase duty
B) Decrease duty
C) Not affect duty
D) Make duty zero
✅ Answer: A
Q37. Which is correct relation?
A) D ∝ Δ
B) D ∝ 1/Δ
C) D ∝ B²
D) D independent
✅ Answer: B
Q38. If base period doubles, delta becomes:
A) Doubled
B) Halved
C) Same
D) Zero
✅ Answer: A
Q39. Which has more duty?
A) Rice
B) Sugarcane
C) Wheat
D) Cotton
✅ Answer: C
Q40. The quantity of water required for a crop is called:
A) Duty
B) Delta
C) CWR
D) Discharge
✅ Answer: C
Q41. Which is true?
A) Delta is independent of crop
B) Duty is independent of crop
C) Delta depends on crop
D) Duty depends only on canal
✅ Answer: C
Q42. If duty is low, water requirement is:
A) Low
B) High
C) Zero
D) Constant
✅ Answer: B
Q43. The relation Δ = 8.64B/D is derived from:
A) Continuity equation
B) Water balance
C) Volume concept
D) Bernoulli equation
✅ Answer: C
Q44. Delta includes:
A) Only evapotranspiration
B) Only rainfall
C) All field losses
D) Only seepage
✅ Answer: C
Q45. Which is not a factor affecting delta?
A) Crop
B) Soil
C) Base period
D) Canal length
✅ Answer: D
Q46. Effective rainfall reduces:
A) Duty
B) Delta
C) Base period
D) Discharge
✅ Answer: B
Q47. High irrigation efficiency results in:
A) Low duty
B) High delta
C) High duty
D) Zero delta
✅ Answer: C
Q48. Which is a numerical trap?
A) Forgetting 8.64
B) Using cm instead of m
C) Wrong base period
D) All of the above
✅ Answer: D
Q49. If delta is zero, crop water requirement is:
A) Maximum
B) Minimum
C) Zero
D) Infinite
✅ Answer: C
Q50. This topic is considered high scoring because:
A) Only theory
B) Only numericals
C) Formula-based
D) No PYQs
✅ Answer: C