Which of the following statements regarding the physical properties of agricultural grains and seeds are CORRECT?
Options:
(A) True density of cereal grains is always strictly greater than their bulk density due to the presence of intergranular void spaces.
(B) For most cereal grains, as moisture content increases within typical storage ranges ($10\%\text{ to }20\%\text{ wb}$), the bulk density decreases while porosity increases.
(C) The filling angle of repose is generally slightly less than or equal to the emptying angle of repose.
(D) Hectoliter test weight is a direct measure of particle true density excluding air voids.
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
Analysis of statements:
- Option A is CORRECT: True density measures the mass per unit volume of the grain kernel alone excluding voids, whereas bulk density includes intergranular voids ($\rho_t > \rho_b$).
- Option B is CORRECT: As grain absorbs water, volumetric expansion of individual kernels is greater than mass increase, and surface friction increases, leading to looser packing. Consequently, bulk density decreases and porosity increases.
- Option C is CORRECT: The angle formed during pile formation (filling angle of repose) is typically $1^\circ\text{--}3^\circ$ smaller than the emptying angle formed when grain drains from an orifice.
- Option D is INCORRECT: Test weight (e.g., hectoliter weight or bushel weight) measures the mass of grain contained in a standard volume with natural packing; it is a measure of bulk density, not true density.