Physical Properties of Soil Questions and Answers

Answer: C

The standard soil texture triangle represents 12 textural classes.

The USDA soil texture triangle plots the percentages of sand, silt and clay on its three sides and divides the area into 12 classes: sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay and clay.

Any soil's position on the triangle, from its laboratory analysis, places it in one of these twelve. The figures 24, 30 and 36 do not correspond to the standard triangle.

Answer: C

The property not affected by organic matter is Soil texture.

Soil texture is the relative proportion of sand, silt and clay, the mineral particles of the soil. It is inherited from the parent material and changes only over very long periods; adding or losing organic matter does not alter it.

The other three depend heavily on organic matter. Humus has a very high cation exchange capacity, organic matter is the food of soil organisms and drives biological activity, and it binds particles into aggregates, improving soil structure.

Answer: A

The bulk density is \(1.35\ \text{g/cm}^{3}\).

Bulk density is the oven-dry mass of soil divided by its total volume:

\[ \begin{aligned} \rho_b &= \frac{\text{dry mass}}{\text{volume}} \\ &= \frac{135\ \text{g}}{100\ \text{cm}^{3}} = 1.35\ \text{g/cm}^{3} \end{aligned} \]

The distractors come from common slips. 1.53 reverses the digits; 13,500 multiplies mass by volume instead of dividing; and 0.75 (strictly about 0.74) is volume divided by mass, which also has the wrong units. A value of 1.35 is typical of a mineral soil.