# Crop Water Requirements

 Question 1
During a particular stage of the growth of a crop, the consumptive use of water is 2.8 mm/day. The amount of water available in the soil is 50 % of the maximum depth of available water in the root zone. Consider the maximum root zone depth of the crop as 80 mm and the irrigation efficiency as 70%.
The interval between irrigation (in days) will be _________. (round off to the nearest integer)
 A 14 B 45 C 58 D 78
GATE CE 2022 SET-1   Irrigation Engineering
Question 1 Explanation:
MTA-Marks to ALL

Frequency =$\frac{\text{Depth of water needed}}{\text{Consumptive use}}=\frac{40}{2.8}=14.28 days$
 Question 2
A reservoir with a live storage of 300 million cubic metre irrigates 40000 hectares ( 1 hectare= $10^{4} \mathrm{~m}^{2}$) of a crop with two fillings of the reservoir. If the base period of the crop is 120 days, the duty for this crop (in hectares per cumec, round off to integer) will then be ________
 A 691 B 127 C 985 D 456
GATE CE 2021 SET-2   Irrigation Engineering
Question 2 Explanation:
\begin{aligned} \text { Live storage } &=300 \mathrm{Mm}^{3} \\ \text { Area } &=40000 \text { hectare }\\ \text {Since 2 filling,} & \text{ so volume of water needed,} \\ &=600 \mathrm{Mm}^{3}\\ B&=120 days \\\text { Duty } &=\frac{8.64 B}{\Delta} \\ \Delta &=\frac{600 \times 10^{6}}{40000 \times 10^{4}}=1.5 \mathrm{~m} \\ \text { Duty } &=\frac{8.64 \times 120}{1.5}=691.2 \text { ha/cumec } \end{aligned}
 Question 3
Crops are grown in a field having soil, which has field capacity of 30% and permanent wilting point of 13%. The effective depth of root zone is 80 cm. Irrigation water is supplied when the average soil moisture drops to 20%. Consider density of the soil as 1500 $kg/m^3$ and density of water as 1000 $kg/m^3$. If the daily consumptive use of water for the crops is 2 mm, the frequency of irrigating the crops (in days), is
 A 7 B 10 C 11 D 13
GATE CE 2020 SET-2   Irrigation Engineering
Question 3 Explanation:
As per GATE Official Answer Key MTA (Marks to All)

FC=30%
PWP=13%

\begin{aligned} d_w&=\frac{\gamma _d}{\gamma _w}d \times (FC-OMC) \\ &= \frac{1500}{1000}\times 80 (0.3-0.2)\\ &= 12cm=120mm \end{aligned}
Consumptive use = 2 mm/day
So, frequency of irrigation =120/2 = 60day
 Question 4
The data for an agricultural field for a specific month are given below:

Pan Evaporation = 100 mm
Effective Rainfall = 20 mm (after deducting losses due to runoff and deep percolation)
Crop Coefficient = 0.4
Irrigation Efficiency = 0.5

The amount of irrigation water (in mm) to be applied to the field in that month, is
 A 0 B 20 C 40 D 80
GATE CE 2020 SET-1   Irrigation Engineering
Question 4 Explanation:
Water required by the crop = 100 x 0.4 = 40mm
Effective rainfall =20mm
Amount of water required after accounting irrigation efficiency $=\frac{20}{0.5}=40mm$
 Question 5
The command area of a canal grows only one crop, i.e., wheat. The base period of wheat is 120 days and its total water requirement, $\Delta$, is 40 cm. If the canal discharge is 2 $m^3/s$, the area, in hectares, rounded off to the nearest integer, which could be irrigated (neglectingall losses) is _______
 A 5184 B 4282 C 2364 D 9852
GATE CE 2019 SET-2   Irrigation Engineering
Question 5 Explanation:
Given data:
Base period, B = 120 days
Delta of crop, $\Delta = 40 cm$
Discharge, $Q = 2 m^3/s$
Area to be irrigated, A = ?
Duty of water, $\Delta =\frac{864 \times B}{\Delta }$ ha/cumec
and Area to be irrigated; A = Q x D
$\Rightarrow A = 2 m^3/s \times \frac{864 \times 120}{40}\; ha/cumec$
$A = 5184\; ha$
 Question 6
The intensity of irrigation for the Kharif season is 50% for an irrigation project with culturable command area of 50,000 hectares. The duty for the Kharif season is 1000 hectare/cumec. Assuming transmission loss of 10%, the required discharge (in cumec, up to two decimal places) at the head of the canal is ______
 A 27.78 B 14.56 C 56.47 D 280.36
GATE CE 2018 SET-2   Irrigation Engineering
Question 6 Explanation:
Culturable command area =50000ha
Intensity of irrigation for kharif season =50 %
$\therefore$ Area under kharif =25000ha
Duty for kharif season =1000 ha/cumec
Duty $=\frac{\text { Area }}{\text { Discharge }}$
$\therefore$ Discharge at the head of field
\begin{aligned} Q &=\frac{25000 \mathrm{ha}}{1000 \mathrm{ha} / \mathrm{cumec}} \\ &=25 \mathrm{cumec} \end{aligned}
Transmission/conveyance loss =10 %
$\therefore \quad \eta_{\text {conveyance }}=90 %$
Discharge at the head of canal
$\begin{array}{l} =\frac{25}{0.9} \text { cumec } \\ =27.78 \text { cumec } \end{array}$
 Question 7
The culturable command area of a canal is 10,000 ha. The area grows only two crops-rice in the Kharif season and wheat in the Rabi season. The design discharge of the canal is based on the rice requirements, which has an irrigated area of 2500 ha, base period of 150 days and delta of 130 cm. The maximum permissible irrigated area (in ha) for wheat, with a base period of 120 days and delta of 50 cm, is
 A 2600 B 5200 C 2500 D 5000
GATE CE 2017 SET-2   Irrigation Engineering
Question 7 Explanation:
\begin{aligned} \mathrm{CCA} &=10000 \mathrm{ha} \\ \text { For rice, } \Delta_{r}&=130 \mathrm{cm}=1.3 \mathrm{m} \\ A_{r} & =2500 \mathrm{ha} \\ B_{r} & =150 \text { days } \\ \text{Duty,}\quad D_{r} & =\frac{8.64 B_{r}}{\Delta_{r}}=\frac{8.64 \times 150}{1.30} \\ D_{r} & =996.923 \mathrm{ha} / \mathrm{cumecs} \\ D_{r} & =\frac{A}{Q} \\ Q & =\frac{2500}{996.923} \mathrm{m}^{3} / \mathrm{s}=2.5077 \mathrm{m}^{3} / \mathrm{s}\\ \text{For wheat also,} &\text{discharge is }2.5077 \mathrm{m}^{3} / \mathrm{s}\\ B_{w} &=120 \text { days } \\ \Delta &=50 \mathrm{cm} \\ A_{w} &=Q \times D_{w} \\ D_{w} &=\frac{8.64 \times B_{w}}{\Delta_{w}} \\ &=\frac{8.64 \times 120}{0.5}=2073.6 \\ \therefore \quad A_{w} &=2.5077 \times 2073.6 \\ &=5199.966 \mathrm{ha} \simeq 5200 \mathrm{ha} \end{aligned}
 Question 8
A field channel has cultivable commanded area of 2000 hectares. The intensities of irrigation for gram and wheat are 30% and 50% respectively. Gram has a kor period of 18 days, kor depth of 12 cm, while wheat has a kor period of 18 days and a kor depth of 15 cm. The discharge (in $m^{3}$/s) required in the field channel to supply water to the commanded area during the kor period is_____.
 A 0.8 B 1.2 C 1.4 D 1.8
GATE CE 2015 SET-2   Irrigation Engineering
Question 8 Explanation:
Gram and wheat are Rabi crops.
So both are grown in the same period.
Discharge required for gram,
$Q_{g}=\frac{A_{g}}{D_{g}}=\frac{2000 \times 0.3}{8.64 \times \frac{18}{0.12}}=0.4630 \mathrm{m}^{3} / \mathrm{s}$
Discharge required for wheat,
$Q_{w}=\frac{A_{w}}{D_{w}}=\frac{2000 \times 0.5}{8.64 \times \frac{18}{0.15}}=0.9645 \mathrm{m}^{3} / \mathrm{s}$
$Total discharge =Q_{g}+Q_{w}=1.4275 \mathrm{m}^{3} / \mathrm{s}$
 Question 9
The two columns below show some parameters and their possible values.

Which of the following options matches the parameters and the values correctly?
 A P-I, Q-II, R-III, S-IV B P-III, Q-VI, R-I, S-V C P-I, Q-V, R-VI, S-II D P-III, Q-II, R-V, S-IV
GATE CE 2015 SET-1   Irrigation Engineering
Question 9 Explanation:
Gross Command Area is measured in hectares.
(P-III)
Duty has a unit of ha/cumec. (R-I)
Delta of wheat can be practically 40 cm
(S- V)
 Question 10
Irrigation water is to be provided to a crop in a field to bring the moisture content of the soil from the existing 18% to the field capacity of the soil at 28%. The effective root zone of the crop is 70 cm. If the densities of the soil and water are 1.3 g/$cm^2$ and 1.0 g/$cm^3$respectively, the depth of irrigation water (in mm) required for irrigating the crop is ________
 A 91 B 81 C 71 D 61
GATE CE 2014 SET-2   Irrigation Engineering
Question 10 Explanation:
Given,
Root zone depth,
$d=70 \mathrm{cm}$
Field capacity,
$F_{C}=28 \%$
Existing moisture content,
$w=18 \%$
Density of soil,
$\gamma=1.3 \mathrm{gm} / \mathrm{cm}^{3}$
Density of water,
$\gamma_{w}=1.0 \mathrm{gm} / \mathrm{cm}^{3}$
Depth of irrigation water required,
\begin{aligned} d_{w} &=\frac{\gamma}{\gamma_{w}} d\left(F_{c}-w\right) \\ &=\frac{1.3}{1.0} \times(70 \times 10)(28 \%-18 \%) \\ &=1.3 \times(70 \times 10) \times \frac{10}{100} \\ &=91 \mathrm{mm} \end{aligned}
There are 10 questions to complete.