# Irrigation Engineering Questions and Answers – Water Requirements of Crops – Estimation of Consumptive Use – 1

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This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Water Requirements of Crops – Estimation of Consumptive Use – 1”.

1. Which formula is extensively used for estimating seasonal water requirements?
a) Blaney-Criddle formula
b) Hargreaves pan evaporation method
c) Penman’s equation
d) Christiansen formula

Explanation: This formula is also used for estimating monthly consumptive use.
Blaney-Criddle formula is written as Cu = k.f where, f = p/40[1.8t + 32].
Where Cu = monthly/seasonal consumptive use, k = crop factor, p = monthly % of annual daylight hours in that period, and t = mean monthly temperature

2. Which method is time-consuming and expensive?
a) Tanks and Lysimeter
b) Vapour transfer method
c) Field plot method
d) Integration method

Explanation: In the Lysimeter method, the plants are grown in the tank with a sand layer at the bottom and a pan for collecting the surplus water. The consumptive use is measured by the amount of water required for the satisfactory growth of plants within tanks. Other methods are more reliable than this method.

3. Which of the following is not an empirical method of determining consumptive use?
a) Lowry Johnson method
b) Penman’s equation
c) Hargreaves method
d) Inflow-outflow method

Explanation: Inflow-outflow method is a direct method in which field observations are made and physical models are used for the purpose. Lowry Johnson, Penman, and Hargreaves method are all empirical methods.

4. The evapotranspiration rate is higher in light green vegetation than in dark green vegetation.
a) True
b) False

Explanation: The production of the rate of absorption of solar energy is high in dark green vegetation hence; its evapotranspiration rate will be higher than that of light green vegetation. The plant diseases causing yellowing of the leaves of the plants greatly reduce evapotranspiration.

5. The monthly consumptive use values for paddy are 26.69, 8.76, 14.38, 22.73, 21.29, 25.50 and 15.06 for the duration of month from June to July. What is the average daily consumptive use?
a) 7.0 mm
b) 8.0 mm
c) 7.5 mm
d) 8.5 mm

Explanation: The total consumptive use for paddy = 29.69 + 8.76 + 14.38 + 22.73 + 21.29 + 25.50 + 15.06 = 137.41 cm
Average daily consumptive use = 137.41 / period of growth in days
= 137.41 / (30+31+31+30+31+30) = 7.5 mm.

6. Which of the following statement is wrong about consumptive use coefficient?
a) It is different for different crops
b) It varies with the crop growth
c) It is different for the same crop at different places
d) It is independent of the crop type and its growth

Explanation: Consumptive use coefficient (k) = evapotranspiration (Cu or Et) / pan evaporation (Ep). It is different for different crops, varies with crop growth and is different at different crop stages for the same crop.

7. What is the range of reflection coefficient for close-grained crops?
a) 0.15-0.25
b) 0.05-0.45
c) 0.05
d) 0.45-0.90

Explanation: The range of reflection coefficient for different surfaces are-

 Close-grained crops 0.15-0.25 Bare lands 0.05-0.45 Water surface 0.05 Snow 0.45-0.90

8. Which method is widely used in India for the computation of consumptive use?
a) Penman’s equation
b) Hargreaves – Christiansen equation
c) Blaney-Criddle equation
d) Tanks and lysimeter

Explanation: The value obtained from Penman’s equation is almost equal to the values obtained from the actual field observations made in pan evaporation method. The values obtained from the Blaney-Criddle equation were on the much higher side (about 30%) and the values obtained from the Hargreaves method is on the lower side (about 15%-20%). Lysimeter method is time-consuming and expensive.

9. The average value of Et/Ep for citrus crops?
a) 0.90
b) 0.7-1.10
c) 0.60
d) 0.66-1

Explanation: Et/Ep ratio is consumptive use coefficient (k). Group F includes citrus fruits like oranges, grapefruit, etc. the Et/Ep ratio is fairly constant throughout the year and average to a value of about 0.60.

10. The monthly consumptive use is given by _____________
a) Cu = k.p/40 [1.8t + 32]
b) Cu = k.p/40 [1.8t – 32]
c) Cu = k.p/40 [t + 32]
d) Cu = k.p/40 [t – 32]

Explanation: BLaney – Criddle formula is used to calculate monthly consumptive use.
Cu = k.p/40 [1.8t + 32] Where, Cu is monthly consumptive use in cm, K = crop factor, T = mean monthly temperature in °C, and P = monthly % of annual day light hours that occur during the period.

11. Determine the pan evaporation from the following data using the Christiansen method.
Extra-terrestrial radiation in cm = 47.3cm
Coefficient of temperature(Ct) = 1.403
Coefficient for wind velocity (Cw)= 1.2
Coefficient for relative humidity (Ch) = 1
Coefficient for percent of possible sunshine(Cs) = 1.073
Coefficient of elevation(Ce) = 1.014
a) 40 cm
b) 30.44 cm
c) 39.8 cm
d) 37.98 cm

Explanation: Christiansen formula for pan evaporation is Ep = 0.459 R.Ct.Cw.Ch.Cs.Ce
Ep = 0.459 x 47.3 x 1.403 x 1.200 x 1.000 x 1.073 x 1.014
= 39.8 cm.

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