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Question 1

There are 5 factors that influence the formation of soil:

Answer 1

1. Parent material (rock type),
   
   2. Organisms (plants, animals, microbes),
   3. Topography (slope of the land, North or South facing, exposure),
   4. Climate (wind, rain, sun, temperature),
2. Time.

Question 2

The general process of soil formation is:

Answer 2

1. Parent material (rock type) begins to disintegrate, caused by weathering
   
   2. Organisms (in particular microorganisms at first) break down and mix parent material and are a source of organic matter
   3. Soil horizons form
2. Soils support stable plant communities

Question 3

There are 3 main types of rock weathering:

Answer 3

1. Physical weathering: abrasion by particles in the wind, impact of rain drops on the rock, the sun heats the rock which then cools at night and during winter, causing the rock to expand and shrink eventually splitting where water and roots then penetrate the rock.
   
   2. Chemical weathering: water and acids on the rock, dissolving some of the particles in the rock, will happen faster in warmer environments.
2. Biological weathering: initially attributed to micro-organisms such as lichens and mosses that excrete organic acids which dissolve the minerals in solid rock. Plant roots can split rocks apart increasing surface area for further physical and chemical weathering.

Question 4

Define the term ‘soil texture’. Particle sizes of stones, sand, silt, clay (using Soil Survey England and Wales classification).

Answer 4

Soil texture is a measurement used to classify mineral soils according to the size of particles in the soil.

Question 5

Definition of Soil Structure

Answer 5

Soil structure refers to the way in which soil particles aggregate (clump together).

Question 6

Formation of Soil Structure

Answer 6

• Environmental factors influence soil aggregation: soils shrink and swell as they absorb and lose water, are subject to freezing, root penetration, and mixing by microorganisms - all of which form small units.
• Proportion of different inorganic soil particles: clay soils aggregate much more strongly than sandy soils.
• Different degrees of soil aggregation; different soil structures:
§ Single Grain (sand),
§ Crumb or Granular,
§ Blocky,
§ Prismatic,
§ Columnar,
§ Platy.

Question 7

Crumb structure, crumb formation and destruction.

Answer 7

• contain a mixture of large and small particles that aggregate to form crumbs, and consequently pores, of all sizes,
• is ideal for horticultural purposes.
The main purpose of soil cultivation is to obtain crumb soil structure