ASRB NET — Farm Machinery & Power / Land & Water Management Engineering / Agricultural Structures & Process Engineering · India · Agricultural Scientists Recruitment Board (ICAR)
Original practice questions written to the published syllabus · not past papersStoring grain and produce safely, the loads it puts on bins and silos, and the conveyors and packages that move and protect it.
In the exams: GATE AG Section 6 (bin/silo pressure in 6 of 8 papers 2019–26); ICAR AICE subject 41 Units 6–7; NCEES PE (ANSI/ASAE S433 supplied); ASRB NET ASPE
ASRB NET — Agricultural Structures & Process Engineering
Storage structures (godowns, bins, silos), grain pressure theories, storage pests and fumigation, material handling equipment and packaging materials, examined as single-answer MCQs with negative marking.
How our questions for ASRB NET spread across the units of Storage Engineering, Material Handling & Packaging. Difficulty: 22 easy, 19 medium, 6 hard.
| Fumigation | 9 | |
| Warehouse management | 8 | |
| Bag and bulk storage | 7 | |
| Causes of storage losses | 6 | |
| Controlled and modified atmosphere storage | 6 | |
| Aeration of stored grain | 4 | |
| Godowns and warehouses | 3 | |
| Janssen's and Airy's theories of bin pressure | 2 | |
| Design of conveyors and elevators | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
What is the purpose of dunnage beneath bag stacks?
B. To keep bags off a floor that transmits ground moisture and allow air below the stack
Dunnage (wooden crates, pallets or polythene sheet) separates the bottom bags from the floor, which may transmit moisture. It does not stabilise the stack by weight or release chemicals.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
In Janssen's theory, the limiting lateral pressure at great depth in a bin depends on
D. Specific weight of grain, hydraulic radius and wall friction coefficient, but not on k
L_max = γR/μ′: k cancels when L = kV is taken to the limit V_max = γR/(μ′k). The vertical limit, by contrast, does depend on k. Depth drops out because the exponential term vanishes.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
Aluminium phosphide tablets release phosphine by reacting with
C. Moisture
AlP + 3H2O → Al(OH)3 + PH3: the reaction is hydrolysis by atmospheric moisture. Oxygen, CO2 and nitrogen do not release the gas.
Further reading: FAO Manual of fumigation for insect control
A 3 g tablet contains 56% aluminium phosphide (AlP, 57.95 g/mol). How much phosphine (PH3, 34.00 g/mol) can it release?
C. 0.99 g
AlP = 3 × 0.56 = 1.68 g = 0.0290 mol; 1 mol AlP gives 1 mol PH3, so PH3 = 0.0290 × 34.00 = 0.99 g (about 1 g). 1.68 g is the mass of AlP, not PH3; 1.76 g ignores the 56% content; inverting the molar mass ratio gives 2.86 g.
Further reading: FAO Manual of fumigation for insect control
A phosphine concentration of 300 ppm (25 °C) is held for 7 days. What is the concentration × time (CT) product in g h m⁻³?
C. 70.1 g h m⁻³
300 ppm = 300 × 34.0/24.45 = 417.2 mg/m³ = 0.4172 g/m³. Time = 7 × 24 = 168 h. CT = 0.4172 × 168 = 70.1 g h m⁻³. Using days instead of hours gives 2.92; using ppm directly gives 50,400 ppm·h, not g h m⁻³; forgetting mg→g gives 70,086.
Further reading: FAO Manual of fumigation for insect control
Why can a contact insecticide sprayed on bag surfaces not replace fumigation of an infested stack?
A. It cannot reach eggs and larvae developing inside kernels
Surface sprays act on insects that walk across treated surfaces; hidden internal stages of primary pests are reached only by a gas that penetrates the grain. Hence sprays are prophylactic and fumigation curative.
Further reading: FAO Manual of fumigation for insect control
Which is used as a carbon dioxide scrubber in CA fruit stores?
C. Hydrated lime, activated carbon or molecular sieve
CO2 is removed by hydrated lime, activated-carbon or molecular-sieve scrubbers. Potassium permanganate absorbs ethylene, not CO2; aluminium phosphide is a fumigant.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops
A condition common to CA, MA and hermetic storage is that
A. It must be gas-tight
Without a seal, air leaks in and the modified atmosphere reverts to air. None requires raised O2, high temperature or prior fumigation.
Grain in hermetic bags is found mouldy at the end of storage although the bags stayed sealed. The most likely cause is
D. The grain was too wet; hermetic storage suppresses insects but cannot make wet grain safe
Hermetic storage kills insects by oxygen depletion, but grain above a safe moisture can still support some fungal activity and quality loss, and anaerobic spoilage can occur. Drying first is a requirement, not an option.
Which conveyor type is best for lifting grain vertically in a compact footprint?
C. Bucket elevator
Bucket elevators lift vertically; belts, horizontal chain and vibratory conveyors move material horizontally or at modest inclines.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
Ten here, 47 in the app. The Laisha app has every practice question we have written to ASRB NET in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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