[Biology Class Notes] on Types of Soil Pdf for Exam

The soil is defined as the organic and inorganic materials on the earth’s surface which provide the medium for the growth of the plants. It slowly develops over time and it is composed of various different materials and it varies due to its composition and structure. It is important for the sustainability of an ecosystem as it serves as the natural medium for vegetation growth. Soil comes under non-renewable resources and its formation is a very slow process.

 

Soil Profile and Soil Horizons:

The soil profile is somewhat similar to that of the soil’s fingerprint. It will differ from other soil samples based on the factors like texture, structure, color, and thickness including its chemical composition.

 

Each layer’s soil profile is referred to as the soil horizon and these horizons can be identified by letters. The upper and the topmost layer of the soil which is the topsoil that we walk on is the Horizon “O”. It is made up of decayed organic stuff which feeds the soil and keeps it healthy and it is one- inch thick. This topmost layer of the soil is said to be the most productive layer and the most fertile part of the soil. This is because it contains busy microorganisms and good hummus that will make the nutrients available for the plants.

 

Horizon “O” will be followed by Horizon “A” which is the next layer of the soil. It is composed of beneficial microorganisms like mycorrhizae and fungi, composed of roots and it is also a part of the topsoil. The microorganisms will feed on the waste materials and be shed off by roots. This layer is said to be the home for earthworms and centipedes which are critters.

 

The next layer will be Horizon “B” which is said to be the tough layer and this soil is so hard that roots or critters cannot penetrate this barrier.

 

Horizon “C” is the next layer, which is the parent material where old soil and rocks that form all the horizons above it. The Horizon “C” layer consists of primary bedrock and secondary materials from other places.

 

Soil Composition and Formation:

The soil is a composition of small pieces of fallen leaves, decomposed tree branches, decayed plants, pieces of broken rock, etc. it is said that the soil stores 0.01% of the total water on Earth’s surface within its nooks, pores, and crannies. Soil contains the following composition: 

• 5% organic matter

• 25% air

• 25% of water

• 45% of minerals

 

An acre of soil can hold nearly 5- 10 tons of living organisms and another interesting fact is that one measly gram of soil will hold about 5000- 7000 bacteria species.

 

Since the soil is composed of different materials and compositions, it affects its formation, colors, and textures too. The soil can be found in colors like yellow, red, and white but the most common colors are brown, black, and gray. The soil could be smooth, rough, creamy, rough, sticky, and crumbly to touch due to the presence of silt, sand, clay, and other mineral particles.

 

Soil takes about 500 years in order to create just an inch of the top layer. Weathering, rains, erosions, floods, thunderstorms, hurricanes, tornadoes, etc are the natural processes that contribute to the formation of the soil.

 

Types of soil:

Soil can be categorized into sandy soil, silty soil, clay soil, peaty soil, saline soil, and loam soil. Following are the classifications

1. Sandy soil:

 

 

Among the different types of soil, sandy soil has the largest particles in it. It feels gritty and dry when touched and this is due to the huge spaces present between the particles and also it will not be able to hold water. Rapidly water drains directly to the places where the roots, especially to those seedlings cannot reach. Since they are carried away by the runoff, plants don’t have a chance of using the nutrients present in this soil efficiently. During the spring season, the top side of the sandy soil is light to work with and also warms quickly. 

 

Moistening the soil and rolling it into a ball in order to check the predominating soil particle are the methods used for testing the soil type. Wet sandy soil when rolled on our palms, there should be no ball formation and it will crumble through our fingers easily. Sandy soil is made up of tiny particles that have been weathered from rocks. It’s also deficient in nutrients and water retention, making it one of the worst sorts of soil for farming.

 

Features

• During strong rains, this type of soil is frequently swept away.

• Because it warms up faster, it carries fewer nutrients for the plants.

• This soil is simpler to cultivate and drains and dries quickly.

 

Applicable To

Potatoes, carrots, lettuce, zucchini, and other vegetables, as well as bulbs and shrubs like Sun roses, Tulips, and Hibiscus, are examples. This dirt is ideal for growing.

 

2. Silty soil:

 

 

When compared to sandy soil, silty soil will be smaller in size and so it will be smoother and it becomes soapy slick when moistened. Silty soil, when rolled between fingers, leaves dirt on our skin. When opposed to sand, silt has smaller particles. It also contains rock and other mineral fragments. It also holds water better than sand because of its fine texture. It is also good for agriculture due to the above-mentioned properties.

 

Even though this soil is fertile, it can’t hold as many nutrients but it can retain water for a longer period of time. It is cold in nature because of its moisture-retention quality and also it can get compacted easily.

 

Features

• If the drainage system is adequately channelized, this provides significant benefits to the plants.

• This soil is easier to cultivate than others.

• It has a soapy, silky texture and tends to hold moisture.

 

Applicable To

If the drainage is adequate, almost any type of fruit and vegetable crop can grow on this soil. This soil is ideal for grasses, perennials, climbers, shrubs, and other plants.

 

3. Clay soil:

 

 

When compared to the above-mentioned soils, clay soil has the smallest particle composition and it has fair water storage qualities. Only a little air can pass through its spaces because of the tiny size of its particles and their tendency to settle together. Plant nutrients will be tightly held due to its slower draining tendency and so this soil is rich in plant food for better growth. clay has the smallest particles. There is extremely little or no airspace since the particles are so closely packed. As a result, water is efficiently retained by this property. However, it becomes difficult for moisture and air to permeate into it, limiting plant growth.

 

During spring, this soil is cold and it will take time to get warm as the water within the soil should also get warmed. When it gets dry, the downside of the soil will be very heavy to work with. Also, it could turn hard and compact during the summer seasons. It feels sticky, rolls up easily, and forms into a sausage-like Shape if moistened. 

 

Features

• It is more difficult to cultivate and warms up slowly in the spring.

• This soil has a poor ability to drain water and has fewer air gaps.

• When dry, this soil is hard and rocky, but when wet, it becomes sticky and bumpy.

 

Applicable To

This soil is ideal for growing ornamental plants and fruit trees. Aster, Helen’s flower, Flowering quince, and other shrubs and perennials thrive in this soil.

 

4. Peaty soil:

 

The color of the peaty soil will be black or dark brown in color. It can be compressed easily due to the presence of high water content in it and feels soft when touched and it is also rich in organic matter. These soil growers use it to regulate the pH levels or soil chemistry as an agent to control the disease for the soil and it also contains acidic water.

 

There will be no ball formation when peat soil is rolled in our palms and when squeezed the water content will be forced out. When touched, this soil will be spongy in nature. Peaty soil can produce good rice crops when drained and fertilized properly.

 

Features

• This black soil has a lot of peat in it, so it’s spongy and moist.

• Because the acidic condition of the soil slows the breakdown process, it provides fewer nutrients.

• This soil heats up quickly and holds water well.

 

Suitable for:

Plants such as legumes, salad crops, root crops, and shrubs such as Witch hazel, Lantern trees, Heather, and others are suitable.

 

5. Saline soil:

 

 

In extremely dry conditions, this soil will usually be brackish due to its high salt content. Saline soil can cause damage and even stall plant growth, cause difficulties in irrigation, and impede germination. 

 

The reason for this soil’s salinity is due to the soluble salts buildup in the rhizosphere. The water uptake by the plants is prevented due to high salt contents and thus leading to drought stress. The easy way to find saline soil is, it would form a white layer coating the surface of the soil and plants grow poorly, they will suffer leaf tip burn which can be especially seen in young leaves.

 

Features

• This type of soil is more stony and grainy than others.

• This soil is frequently found on a bedrock of limestone or chalk.

• The alkaline composition of this soil might cause yellowing leaves and stunted plant development in some cases.

 

Applicable To

Cabbage, sweet corn, spinach, beets, and other vegetables Pinks, Lilacs, Mock Oranges, Weigela, Madonna Lillie, and other bulbs, trees, and bushes

 

6. Loam soil:

 

 

Loam soil is said to be the ideal type of soil as the gardens and gardeners just love it. The three materials like silt, clay plus hummus, and sand are balanced present in this soil. Due to its previous organic matter content, it will have higher calcium and pH levels.

 

The color of this soil is dark and it is dry and crumbles when touched. Between the soil particles, the air moves freely down to the roots.

 

It has the ideal proportions of each type of soil and hummus, both of which are required to supply nutrients for growth. Because sand, silt, and clay combine to offer beneficial properties, loam soils are optimal for plant growth. For starters, the different-sized particles create openings in the soil for air, water, and roots to pass through. The minerals in the suspended water provide food for the roots. As a result, loamy soil is thought to be the greatest soil for gardening and farming.

 

Features

• This soil is made up of a combination of silt, clay, and sand.

• This soil is easy to cultivate and warms up quickly, without becoming too dry during the warmer months. This is an excellent soil for growing plants outside.

• It’s fine-textured, moist soil.

 

Applicable To

This soil supports almost all types of fruit and vegetable crops. In this soil, bamboos, climbers, perennials, tubers, and shrubs like Dog’s tooth violets, Wisteria, Rubus, and others thrive.

 

How to find out the type of soil in your garden?

In order to find out the type of soil without getting your hands dirty, just fill the soil sample in a jar, shake vigorously, and allow the soil to settle overnight. The very next day, distinct layers of the soil can be seen. Clay will remain at the top, followed by silt and then sand at the bottom layer.

 

Soil Erosion and Resistance to Erosion:

By the actions of flowing water, the force of gravity, ice, or wind, the soil profiles will be continuously disrupted. The soil particles from “A” horizons are removed and expose the horizons’ subsurface to weathering, plant nutrients, resulting in humus loss and beneficial to the organisms of the soil.

 

Depending upon the texture and topographic characteristics of the soil, lies the soil’s ability to resist wind and water erosion. Due to the strong cohesive forces between the particles and the glue-like characteristics of the hummus, the clay-rich soil can resist erosion. Loam soil has sufficient clay content in order to hold the particles together and sandy soils have high permeability limits so both the soils are moderately resistant. Due to the low permeability value, the silty soils can exhibit the least resistance to soil erosion.

 

Deposition of soil and erosion of soil is the natural geomorphic process that gives shapes to the landforms and in order for the development of soil profiles, it provides new parent material. Knowledge of actual and acceptable rates of soil erosion is required for the development of soil conservation.