Question

The range of 2.6-2.7 Mg.m$^{-3}$ represents the following:

• A. Mean particle density of most organic soils
• B. Mean particle density of most mineral soils
• C. Mean bulk density of most organic soils
• D. Mean bulk density of most mineral soils

Hint:

Always keep in mind:
Standard average value for mineral soil particle density = \( 2.65 \text{ g/cm}^3 = 2.65 \text{ Mg/m}^3 \).
Bulk density is always lower than particle density and is typically around \( 1.33 \text{ g/cm}^3 \) (assuming 50% porosity).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Particle density ($\rho_p$) is the mass of dry soil solids divided by the volume of the soil solids (excluding pore space).
Bulk density ($\rho_b$) is the mass of dry soil solids divided by the total volume of the soil (including both solids and pores).
Detailed Explanation:
- Most common mineral soils are composed of quartz, feldspar, and clay minerals.
- The density of quartz, which is the dominant mineral in soil, is approximately $2.65 \text{ g/cm}^3$ (which is equivalent to $2.65 \text{ Mg/m}^3$).
- Since most mineral soils are composed of these minerals, their average particle density consistently falls within a narrow range of ______2.6 to 2.7 Mg/m$^{-3}$______.
- In contrast, organic soils contain significant amounts of organic matter, which has a much lower particle density (typically $1.2 \text{ to } 1.5 \text{ Mg/m}^3$).
- The bulk density of mineral soils is much lower than the particle density because it includes pore space (typically $1.3 \text{ to } 1.6 \text{ Mg/m}^3$).

Step 2: Final Answer:
The range $2.6 \text{ to } 2.7 \text{ Mg/m}^{-3}$ represents the mean particle density of most mineral soils. This corresponds to option (B).