Soil Assignment #1

Name and explain the method (steps) used for a field soil texture test.

1. Take a sample of soil sufficient to comfortable fit in the palm of your hand. 2. Moisten the soil with a bit of water. 3. Roll into a ball. 4. Ribbon the soil ball by pressing it between your thumb and forefinger until it breaks.

Explain the four step method used to carry out a slaking test.

1. Take soil samples (usually only surface soil is tested for slaking) and allow them to air dry for 1 to 5 days, depending on how dry or wet the soil is. 2. Take several (at least three) small (3 to 5 mm diameter) crumbs of dry soil and place them in a dish or saucer of rainwater (or distilled water) deep enough to completely cover the samples. 3. Cover the dish to prevent wind from disturbing the water. 4. Assess the slaking score (0-4) after 5 minutes.

Explain the four step method used to carry out a dispersion test.

1. Take soil samples (usually only surface soil is tested for slaking) and allow them to air dry overnight. 2. Take several (at least three) small (3 to 5 mm diameter) crumbs of dry soil and place them in a dish or saucer of rainwater (distilled water) deep enough to completely cover the samples. 3. Cover the dish to stop wind disturbing the water. 4. Assess the dispersion score (0-4) after 10 minutes and 2 hours.

Horizon layer R - Bedrock

A mass of rock such as granite, basalt, quartzite, limestone or sandstone that forms the parent material for some soils - if the bedrock is close enough to the surface to weather. This is not soil and is located under the C horizon.

What is surface crusting?

As the muddy soil surface dries out, it crusts over. Structural crusts range from a few tenths to as thick as two inches. A surface crust is much more compact, hard and brittle when dry than the soil immediately beneath it, which may be loose and friable.

What is meant by the term dispersion?

Dispersion (the separation of soil into single particles) is governed by soil texture, clay type, soil organic matter, soil salinity and exchangeable cations. The dispersion index that is calculated here combines dispersion on wetting (immersing an air-dry aggregate in water), and dispersion after remoulding (immersing a piece of soil in water that has been kneaded and worked while moist). Slaking and dispersion are soil characteristics that will have a large influence on the behaviour and management of a soil.

Horizon layer E - Eluviated

Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials - missing in some soils but often found in older soils and forest soils.

Describe an ideal soil for a vegetable production system or landscape plants.

Loamy or sand clay loam.

Most soils have how many major horizons?

Most soils have three major horizons (A, B, C) and some have an organic horizon (O).

Horizon layer A - Topsoil

Mostly minerals from parent material with organic matter incorporated. A good material for plants and other organisms to live.

Horizon layer O - Humus or organic

Mostly organic matter such as decomposing leaves. The O horizon is thin in some soils, thick in others, and not present at all in others.

N

Nitrogen = Leafy greens

What are the six different layers of horizons?

O - (humus or organic) A - (topsoil) E - (eluviated) B - (subsoil) C - (parent material) R - (bedrock)

P

Phosphorous = Strong root growth

K

Potassium = Flowers & Fruits

Horizon layer B - Subsoil

Rich in minerals that leached (moved down) from the A or E horizons and accumulated here.

What is meant by the term slaking?

Slaking is the breakdown of a lump of soil into smaller fragments on wetting. It is caused when clay swells and the trapped air bursts out. Organic matter reduces slaking by binding mineral particles and by slowing the rate of wetting. This process occurs in all soil groups of the main vegetable-growing districts.

Explain how soil structure can be improved under field conditions?

Soil structure can be improved by adding organic matter and compost, which help hold the particles together like a glue.

What is soil structure?

Soil structure refers to the arrangement of soil separates into units called soil aggregates. An aggregate possesses solids and pore space. Aggregates are separated by planes of weakness and are dominated by clay particles. Silt and fine sand particles may also be part of an aggregate.

Identify properties that influence the water holding capacity of soil.

Soil water holding capacity is controlled primarily by the soil texture and the soil organic matter content. In general, the higher the percentage of silt and clay sized particles, the higher the water holding capacity. As the level of organic matter increases in a soil, the water holding capacity also increases, due to the affinity of organic matter for water.

Horizon layer C - Parent Material

The deposit at Earth's surface from which the soil developed.

What is the main difference between organic and chemical fertilisers?

The percentage of total nutrients that are immediately soluble in water - except for some of the phosphorous and sulphur, the nutrients in most 'chemical' fertilizers are completely soluble in water, whereas only a portion of the nutrients in organic fertilizers is immediately soluble in water

What is a soil profile and what can it be used for?

The soil profile is defined as a vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock. The soil profile is one of the most important concepts in soil science. It is a key to understanding the processes that have taken in soil development and is the means of determining the types of soil that occur and is the basis for their classification.

What is soil texture?

The texture of a soil determines soil water-holding capacity, permeability, and soil workability. Sand, silt, clay, and organic matter particles in a soil combine with one another to form larger particles.

What are soil horizons?

Virtually all soil profiles are composed of a number of distinctive layers, termed horizons, interpretation of which is the key to understanding how the soil has formed. There are different types of soil, each with its own set of characteristics. Dig down deep into any soil, and you'll see that it is made of layers, or horizons (O, A, E, B, C, R). Put the horizons together, and they form a soil profile. Like a biography, each profile tells a story about the life of a soil.