BCS Agriculture cadre — Agricultural Engineering (subject code 821) · Bangladesh · Bangladesh Public Service Commission
Original practice questions written to the published syllabus · not past papersDesigning and evaluating sprinkler and drip systems, from emitter hydraulics to pump selection.
In the exams: GATE AG Section 5 (sprinkler in 4 of 8, drip in 3 of 8 papers 2019–26); ICAR AICE subject 43 Unit 4; NCEES PE irrigation; IA CID (General Ag, Drip/Micro and Sprinkler exams)
How our questions for BCS Agriculture cadre spread across the units of Sprinkler & Micro-Irrigation Systems. Difficulty: 30 easy, 15 medium, 0 hard.
| Drip system components | 6 | |
| Sprinkler types and components | 5 | |
| Sprinkler spacing and application rate | 4 | |
| Filtration | 4 | |
| Economics of pressurised irrigation | 4 | |
| Christiansen's uniformity coefficient | 3 | |
| Sprinkler lateral and main design | 3 | |
| Allowable pressure variation and the friction factor F | 3 | |
| Fertigation | 3 | |
| Automation | 3 | |
| Emitter hydraulics: exponent and coefficient of variation | 2 | |
| Drip lateral and sub-main design | 2 | |
| System layout and pump selection | 2 | |
| Emission uniformity | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Sprinklers discharging 0.5 L/s each are spaced 12 m along the lateral and 18 m between laterals. What is the average application rate?
D. 8.33 mm/h
I = 3600 q / (Sl × Sm) = 3600 × 0.5 / (12 × 18) = 8.33 mm/h (1 L over 1 m² is 1 mm). Using 1000 instead of 3600 (treating L/s as m³/h) gives 2.31; adding the spacings instead of multiplying gives 60; using 12 m × 12 m gives 12.5.
Further reading: Michael, Irrigation: Theory and Practice
Eight catch cans between sprinklers collect 10, 12, 9, 11, 8, 12, 10 and 8 mm. What is Christiansen's uniformity coefficient?
D. 87.5 %
Mean = 80/8 = 10 mm. Absolute deviations 0, 2, 1, 1, 2, 2, 0, 2 sum to 10 mm. CU = 100 (1 − 10/(8 × 10)) = 87.5 %. 80 % is the low-quarter DU; 85.0 % uses the standard deviation (a different coefficient). 12.5 % is the deviation ratio 10/80 itself, not 100 (1 − 10/80).
Further reading: Michael, Irrigation: Theory and Practice
Why do labyrinth (tortuous-path) emitters allow a larger flow passage than long-path laminar emitters for the same discharge?
D. The zigzag path creates turbulence that dissipates head in a shorter, wider channel
In a tortuous path, repeated changes of direction dissipate energy through turbulence, so a wider, shorter channel achieves the same head loss; this reduces clogging risk and makes x close to 0.5. A long laminar path needs a very narrow, long channel.
Further reading: Lamm, Ayars and Nakayama, Microirrigation for Crop Production
Drip laterals are most commonly made of which material?
B. Polyethylene
Laterals are flexible polyethylene tubing (commonly LLDPE/LDPE blends) because it is cheap, flexible, resistant to fertilisers and allows emitters to be inserted or moulded in. Aluminium is used for portable sprinkler laterals; PVC is common for buried mains.
Further reading: Michael, Irrigation: Theory and Practice
An emitter exponent x = 1.0 indicates which flow regime?
A. Fully laminar flow
Laminar flow through a long, fine passage makes discharge proportional to head (x = 1). Fully turbulent orifice flow gives x = 0.5, vortex emitters about 0.4, and pressure-compensating emitters approach zero.
Further reading: Keller and Bliesner, Sprinkle and Trickle Irrigation
In an older drip system that was designed with a high emission uniformity, what is usually the main reason field EU has fallen?
C. Emitter clogging
Physical, chemical and biological clogging reduces flow unevenly and is the dominant cause of declining uniformity. Water treatment, filtration and flushing are the remedies.
Further reading: Lamm, Ayars and Nakayama, Microirrigation for Crop Production
Which filter is effective for removing sand from well water but ineffective against algae and organic matter?
B. Hydrocyclone (centrifugal sand separator)
A hydrocyclone separates particles denser than water by centrifugal action; algae and organic matter have densities close to water and pass through. Media filters are preferred for organic loads.
Further reading: Lamm, Ayars and Nakayama, Microirrigation for Crop Production
Which pair of fertilisers must not be mixed in the same concentrated stock tank because a precipitate forms?
C. Calcium nitrate and a sulphate or phosphate fertiliser
Calcium reacts with sulphate to form gypsum and with phosphate to form calcium phosphates, both of low solubility; they are kept in separate A and B tanks. The other pairs are compatible in normal stock concentrations.
Further reading: Lamm, Ayars and Nakayama, Microirrigation for Crop Production
When dividing a drip field into irrigation shifts (zones), what is the main hydraulic aim?
B. Shifts of about equal flow so the pump always runs near its design point
Equal-flow shifts keep the pump at the same operating point and efficiency for every shift. Equal area is not enough when crops or emitter densities differ.
Further reading: Keller and Bliesner, Sprinkle and Trickle Irrigation
What does the economic pipe size minimise?
D. The sum of annualised pipe cost and annual pumping energy cost
Larger pipes cost more but save energy by reducing friction. The economic size is the one with the least total annual cost; minimising pipe cost alone leads to high energy bills, and minimising friction alone leads to oversized pipes.
Further reading: Keller and Bliesner, Sprinkle and Trickle Irrigation
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