LESSON 2: TYPES OF SOIL, THEIR DIFFERENCES AND PROPERTIES.

TYPES OF SOIL

Sand, silt, and clay are the basic types of soil. Most soils are made up of a combination of the three. The texture of the soil, how it looks and feels, depends upon the amount of each one in that particular soil. The type of soil varies from place to place on our planet and can even vary from one place to another in your own backyard.

Soil Types

People describe soil types in all kinds of ways such as heavy, light, sandy, clay, loam, poor or good. Soil scientists describe soil types by how much sand, silt and clay are present. This is called texture. It is possible to change the texture by adding different things. Changing texture can help in providing the right conditions needed for plant growth.

Sand is the largest particle in the soil. When you rub it, it feels rough. This is because it has sharp edges. Sand doesn't hold many nutrients.

Silt is a soil particle whose size is between sand and clay. Silt feels smooth and powdery. When wet it feels smooth but not sticky.

Clay is the smallest of particles. Clay is smooth when dry and sticky when wet. Soils high in clay content are called heavy soils. Clay also can hold a lot of nutrients, but doesn't let air and water through it well.

Particle size has a lot to do with a soil's drainage and nutrient holding capacity. 

To better understand how big these three soil particles are, think of them like this. If a particle of sand were the size of a basketball, then silt would be the size of a baseball, and clay would be the size of a golf ball. Line them all up, and you can see how these particles compare in size.

 Loam is soil composed of sand, silt, and 

clay in relatively even concentration 

(about 40-40-20% concentration 

respectively).^[1] These proportions can 

vary to a degree however, and result in 

different types of loam soils: sandy loam, 

silty loam, clay loam, sandy clay loam, 

silty clay loam, and loam.^[1] Loam soils 

generally contain more nutrients, moisture 

and humus than sandy soils, have better 

drainage and infiltration of water and air 

than silty soils, and are easier to till than 

clay soils. The different types of loam 

soils each have slightly different 

characteristics, with some draining 

liquids more efficiently than others.

Loam: 

LESSON ONE: MEANING OF SOIL AND IT'S PHYSICAL COMPOSITION

WHAT IS SOIL?

Soil is the uppermost layer of the earth crust on which plants grow.

Soil is a thin layer of material on the Earth's surface in which plants have their roots. It is made up of many things, such as weathered rock and decayed plant and animal matter. 

Soil is formed over a long period of time. Soil Formation takes place when many things interact, such as air, water, plant life, animal life, rocks, and chemicals.

                                                               

VERY GOOD SOIL

SOIL COMPOSITION

Soils are a mixture of different things; rocks, minerals, and dead, decaying plants and animals. Soil can be very different from one location to another, but generally consists of organic and inorganic materials, water and air. 

The inorganic materials are the rocks that have been broken down into smaller pieces. The size of the pieces varies. It may appear as pebbles, gravel, or as small as particles of sand or clay. The organic material is decaying living matter. 

This could be plants or animals that have died and decay until they become part of the soil. The amount of water in the soil is closely linked with the climate and other characteristics of the region.

 The amount of water in the soil is one thing that can affect the amount of air. Very wet soil like you would find in a wetland probably has very little air. The composition of the soil affects the plants and therefore the animals that can live there.

                                               

                                                              

                                                   

Soil is made up of an extensive variety of substances, minerals and rocks. These substances can be categorized into four main groups. These groups are organic materials, inorganic materials, air and water.

SOIL FORMATION

The formation of soil happens over a very long period of time. It can take 1000 years or more.

 Soil is formed from the weathering of rocks and minerals. The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter. 

Over time this creates a thin layer of soil. Plants help the development of the soil. How? The plants attract animals, and when the animals die, their bodies decay. Decaying matter makes the soil thick and rich. This continues until the soil is fully formed. The soil then supports many different plants.

Weathering:

Weathering is the process of the breaking down rocks. There are two different types of weathering. Physical weathering and chemical weathering.
In physical weathering it breaks down the rocks, but what it's made of stays the same. In chemical weathering it still breaks down the rocks, but it may change what it's made of. For instance, a hard material may change to a soft material after chemical weathering.

Stages in the Formation of Soil

                                                       

SOIL PROFILE

Soil Profile refers to the layers of soil; horizon A, B, and C. If you're wondering what horizon A is, here's your answer: horizon A refers to the upper layer of soil, nearest the surface. It is commonly known as topsoil. 

In the woods or other areas that have not been plowed or tilled, this layer would probably include organic litter, such as fallen leaves and twigs . The litter helps prevent erosion, holds moisture, and decays to form a very rich soil known as humus. Horizon A provides plants with nutrients they need for a great life.

The layer below horizon A, of course, has to be horizon B. Litter is not present in horizon B and therefore there is much less humus. Horizon B does contain some elements from horizon A because of the process of leaching. Leaching resembles what happens in a coffee pot as the water drips through the coffee grounds. Leaching may also bring some minerals from horizon B down to horizon C.

If horizon B is below horizon A, then horizon C must be below horizon B. Horizon C consists mostly of weatherized big rocks. This solid rock, as you discovered in soil formation, gave rise to the horizons above it.