Soil Science

Revision

 
 

In the ribbon test for field texture, what ribbon length is associated with a loam??

Correct! 25 mm. While few people bother to learn all the ribbon lengths, this is one worth remembering. A loam is a mid range texture and contains roughly equal quantities of coarse sand, fine sand, silt and clay. A sandy loam has more sand (and a shorter ribbon), and a clay loam has more clay (and a longer ribbon).

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A ped which was 200 mm tall, 75 mm deep and wide, with relatively flat faces and sharp edges would be described as:?

Correct!

Try again. Prismatic. If you got this wrong, revise the Field Structure section.

  

Which of the following soil structures occurring near the soil surface would be a clue that compaction had occurred??

Correct! Platy structures are often associated with compacted layers in soils. Compaction can also lead to small peds being welded together to create large ones, as well as a massive structure where no peds are apparent at all.

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A surface mineral horizon that is darkened by organic matter would be called a?

Correct! A1 horizon. O horizons are composed of organic matter (ie decomposing plant residues) rather than minerals. A2 horizons are pale.

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The correct moisture content for the ribbon test for field texture is?

Correct! When the soil just fails to stick to the hand. This is called the sticky point and approximates field capacity moisture content. It is essential to have the correct moisture content, as moisture affects the length of the nbbon.

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A horizon of weathered rock in the lower part of the soil is most likely to be a?

Correct! C horizon. If you got this wrong, revise the Soil Horizons screen.

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