Soil Science

Revision

 
 

Which of the following properties is least affected by soil texture??

Correct! Soil texture affects cation exchange capacity, plant available water and aggregation but has little influence on soil colour.

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Particle size analysis is based on:?

Correct! Stokes' Law describes the terminal velocity of particles falling through a fluid, where the velocity is proportional to the square of the diameter of the particles. Stokes' Law is applicable for particles with diameters in the range 0.2 pm - 0.2 mm.

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A clay-textured soil is likely to have a?

Correct! Because of the large surface area of particles, clay-textured soils usually have a high cation exchange capacity, and a high moisture content when the soil is air-dry. Clay-textured soils uswally have a low saturated hydraulic conductivity and high water content at field capacity.

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In a particle size analysis, a 50 g soil sample (at the oven-dried moisture content) yields 10 g coarse sand, 20 g silt + clay and 10 g clay. What is the proportion of fine sand??

Correct! The yield of fine sand is calculated by difference to be 20 g, which is 40% of the sample.

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Particle size analysis shows that a soil sample has 30% clay, 50% silt and 20% sand. The texture class for this soil is:?

Correct! All textural classes with more than 30% silt use the adjective 'silty' in the textural class name.

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Particle size analysis shows that a soil sample has 10% clay, 10% silt and 80% sand. The texture class for this soil is:?

Correct! From the percentages of sand, silt and clay, the soil obviously has a very coarse texture. Of the options given, loamy sand has the coarsest texture and is the correct texture class

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