IMPORTANCE OF SOIL

WHAT IS SOIL?

Soil is the upper layer of earth in which plants grow. It is a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles.

It is one of the three major natural resources, alongside air and water. It is one of the marvelous products of nature and without which there would be no life at all.

It is made up of three main components-

Minerals or inorganic matter that come from rocks below or nearby, water and air and organic matter which includes the remains of plants and animals (humus)  and the living organisms including microscopic bacteria and fungi that live in the soil. The proportion of each of these is important in determining the type of soil that is present. 

 Below is a diagram showing the percentage composition of loamy soil.

 Soil composition of loamy soil.

 

(http://www.physicalgeography.net/fundamentals/10t.html)

(https://www.soil-net.com/legacy/schools/what_is_soil1.htm)

https://www.google.co.za/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=WHAT+IS+SOIL

https://www.soil-net.com/legacy/schools/what_is_soil1.htm

UPLOADED BY JOE PEPLER

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WHAT IS SOIL TEXTURE

Soil texture: is how rough or smooth the soil feels when you rub a moist sample of it between your fingers. Soil texture depends on the proportion of small and large rock particles in the soil.

Soil texture refers to the weight proportion (relative proportion by weight percentage of sand, silt, and clay) of the mineral soil separates for particles less than two millimeters (mm) as determined from a laboratory particle-size distribution.

Soil texture and structure

·        https://intranet.bishops.org.za/Biology/Grade9/index.htm grade 9 notes.

UPLOADED BY: JONATHAN BORDER

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AIR CONTENT OF SOIL

Soil texture determines how much air is in the soil and how water moves through the soil – which is essential for plant growth. Air content is the amount of air in the soil. Air is found in spaces called pores between the rock particles in the soil. These pores can be filled with water or air or both.

 Air is important in soils because the organisms that break down the organic matter in the soil need oxygen for respiration. Plant roots need oxygen for respiration. Soil texture determines the amount of air in a soil. Clay soils have small rock particles and therefore small pores and little space for air. Sandy soils have large rock particles and large spaces for lots of air. One way to identify different types of soil is to add water and allow the layers to separate. (See Figure

Below is a diagram showing how the layers of different sized soil settle in water in a jar. (We will use test tubes or measuring cylinders)

About half of the total mass of soil is made of up vast, interconnecting cavities, or holes. These holes are filled with both air and water. The amount of air and the amount of water filling these spaces varies dramatically throughout the year and from location to location, but averages about 50% each.

References:

·        https://www.google.co.za/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=the+Air+Content+of+soil

·        https://intranet.bishops.org.za/Biology/Grade9/index.htm grade 9 notes.

·        http://sjrp1.weebly.com/science.html

UPLOADED BY JONATHAN BORDER

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WHY IS SOIL SO IMPORTANT?

Healthy soil gives us clean air and water, crops and productive grazing lands, diverse wildlife, and beautiful South African landscapes. Soil does all this by performing seven essential functions:

1.   Soil serves as the medium for growing all kinds of plants.

2.   Soils modify the atmosphere by emitting and absorbing gases (carbon dioxide, methane, water vapour) and dust.

3.   Soils provide habitats for animals to live in, from mice to microscopic bacteria.

4.   Soils hold, release, alter and purify most of the water in terresterial systems.

5.   Soils act as a fliter to clean water before it moves to undeground storage (an aquifer).

6.   Soils process recycled materials, including carbon, so that living things can use them over and over again.

7.   Soils serve as engineering media for construction of foundations, roadbeds, dams and buildings and preserve artifacts of human history and archaeology.

What are soil types related to particle size?

The rock particles in the soil range in size from very small particles (clay) to medium sized particles (silt) to large particles (sand).

·         Soil that contains mostly clay particles is called clay soil and has a smooth texture. Clay soils hold a lot of water, but little air.

·         Soils that have mainly sand particles are called sandy soils and have a rough texture. Sandy soils do not hold much water, but contain a lot of air.

·         Silt is a combination of sand, clay and other materials.

·         Loam soil is a fertile soil containing a mixture of sand and humus. Humus is decomposing organic matter formed when bacteria and fungi break down dead plant and animal matter in the soil. Humus provides the nutrients that plants need, improves the water retention capacity of the soil. Loam soils have a good balance of air and water in them and are the most suitable soil type for plant growth.

·         Garden soil is soil in a home garden which has its own unique texture and combination of sand, silt, clay and various minerals. A good garden soil should have a high proportion of humus in it.

·         Potting soil or potting mix is a medium used to grow plants, herbs and vegetables and usually contain peat, composted bark, sand and perlite (industrial mineral). Little or no soil is actually found in potting soil.

http://www.rodalesorganiclife.com/garden/10-easy-soil-tests

UPLOADED BY LAWRENCE MASHA

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What are soil types related to particle size?

There are 6 types of soil:

·        Clay soil

·        Silt

·        Sandy soil

·        Loam soil

·        Garden soil

·        Potting soil

Clay soil- Is soil made mostly of clay particles, clay soil has a smooth texture, clay soil hold a lot of water particles and little air particles.

Silt- Silt is a combination of clay particles, water particles and other material.

Sandy soil- Are soils made mostly of sand particles, sandy soils hold little water particles and a lot of air, sandy soils have a rough texture.

Loam soil- is a fertile soil containing sand and humus, loam soil has a good balance between air and water, this is one of the best soils for planting.

Garden soil- this soil is found in a household garden; it is made of a combination of sand silt and clay, garden soil has a unique texture.

Potting soil- potting soil is also known as potting mix; it is used to plant herbs, vegetables and plants; potting soil usually contains bark, sand, perlite and peat (little to none soil is found in potting soil)

References: Biology term 1 notes

UPLOADED BY: GABRIEL DE GRAAF

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Water Holding Capacity

The water holding capacity of a soil is a very important agronomic characteristic. Soils that hold generous amounts of water are less subject to leaching losses of nutrients or soil applied pesticides. This is true because a soil with a limited water holding capacity (i.e. a sandy loam) reaches the saturation point much sooner than a soil with a higher water holding capacity (i.e. a clay loam). After a soil is saturated with water, all of the excess water and some of the nutrients and pesticides that are in the soil solution are leached downward in the soil profile.

Soil water holding capacity is controlled primarily by the soil texture and the soil organic matter content. Soil texture is a reflection of the particle size distribution of a soil. An example is a silt loam soil that has 30% sand, 60% silt and 10% clay sized particles. In general, the higher the percentage of silt and clay sized particles, the higher the water holding capacity. The small particles (clay and silt) have a much larger surface area than the larger sand particles. This large surface area allows the soil to hold a greater quantity of water. The amount of organic material in a soil also influences 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.

 (agvise, 1977)

http://soilquality.org.au/factsheets/water-availability

http://msue.anr.msu.edu/news/why_is_soil_water_holding_capacity_important

UPLOADED BY GREG MEDCALF