Soil PDF

starts with Gardening good soil. il? What is so 8 Chapter Soil...

starts with Gardening good soil. il? What is so 8 Chapter Soil By the end of this chapter, you should be able to: describe the characteristics of soil horizon and the process of soil formation from the model including identify the factors that make the characteristics and properties of soils different. measure some properties of soils by using appropriate tools and present the guidelines for the use of bene ts of soil based on the data of soil properties.  8.1 Soil Components of soil Soil is a mixture of inorganic materials, organic materials, air, water and soil organisms. The inorganic materials found in the soil is the weathered rocks which are made up of minerals combined in different ways. The organic materials are the decaying living matter. This could be plants or animals that have died and decayed 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 affects the amount of air. Very wet soil like those in a wetland probably has very little air. The composition of the soil affects the types plants that can grow on the soil and therefore the animals that can live there.  Types of soil There are three basic types of soils, namely clay soil, loamy soil and sandy soil. Loamy soil is the ideal. The other two soil types present challenges for irrigation. How do you find out which type of soil you have? Pick up a marble-sized chunk of moist soil and roll it between your thumb, forefinger and middle finger, as if trying to shape it into a little ball. If your rolling is successful and you end up with a ball with the size of a marble, then your soil is clay soil. If your attempt at forming a ball is completely unsuccessful and the soil falls apart, then your soil is sandy soil. If your attempt at forming a ball is not so successful and the ball falls apart once you apply a gentle pressure on it, then your soil is loamy soil. Most soils are made up of a combination of the three. 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. 148 Science Focus Smart MATHAYOM 2 Soil properties A Soil color In general, the darker a soil is, the more nutrient it has. The darker colored soil usually contains more decomposed organic matter known as humus. Gray soils often indicate poor drainage while red soils can indicate very poor soils. These are the general rules about soil colors. Under certain conditions, a very poor soil can appear as dark black, while a rich healthy soil can appear as red. B Soil texture Soil texture refers to the proportion of the sand, silt, and clay in the soil. The size ranges of sand, silt and clay are as follows: Type of soil Size range Sand 0.05 mm to 2 mm Silt 0.002 mm to 0.05 mm Clay Less than 0.002 mm Sand, silt, and clay represent the inorganic soil particles less than 2 mm in diameter. Inorganic soil particles of 2 mm in size or larger are called rock fragments or gravel and pebbles. Soil texture is important in determining the amount of water retained by the soil and air movement. Fine-textured soil retains more water and has lesser air movement than the coarse-textured soil, but it may be not ideal for plant growth. The texture of the soil, how it looks and feels, depends upon the amount of sand, silt and clay. Soil texture can affect the amount of pore space within a soil. Sand-sized soil particles fit together in a way that create large pores. Clay-sized soil particles fit together in a way that create small pores. arger maller pore pore   Chapter 8 149 Soil  C Soil structure Have you ever played with a dirt clod? A dirt clod is a small clump of soil that has formed a rock-like clump. These dirt clods are called peds by geologists. Soil ped is the basic unit of soil structure. These peds are organized into a repeating pattern that is referred to as soil structure. Between the peds are cracks called “pores” through which soil, air and water are conducted. Soil structure is most commonly described in terms of the shape of the individual peds that occur within a soil horizon. There are a few types of soil structure. Granular – roughly spherical, like cookie crumbs. Usually 1 to10 mm in diameter. Most common in horizon A, where plant roots, microorganisms and sticky products of organic matter decomposed bind soil grains into granular aggregates. Platy – flat peds that lie horizontally in the soil. Platy structure can be found in horizon A, B and C. It commonly occurs in horizon A as the result of compaction. Blocky – roughly cube-shaped, with more or less flat surfaces. Sizes commonly range from 5 to 50 mm across. Blocky structures are typical of horizon B, especially those with a high clay content. They form by repeated expansion and contraction of clay minerals. Prismatic – larger, vertically elongated blocks, often with five sides. Sizes are commonly 10 to 100 mm across. Columnar – the units are similar to prisms and are bounded by flat or slightly rounded vertical faces. The tops of columns, in contrast to those of prisms, are very distinct and normally rounded.   150 Science Focus Smart MATHAYOM 2 There are two types of ‘structureless’ soil. Massive – compact, coherent soil, not separated into peds of any kind. Massive structures in clay soils, usually have very small pores, slow permeability and poor aeration. Single grain – in some very sandy soils, every grain acts independently, and there is no binding agent to hold the grains together into peds. Permeability is rapid, but fertility and water holding capacity are low.     D Soil consistency Soil consistency refers to the ease with which an individual ped can be crushed by the fingers. Soil consistency depends on soil moisture content. Moist soil: loose – non-coherent when dry or moist; does not hold together in a mass. friable – when moist, crushed easily under gentle pressure between thumb and forefinger and can be pressed together into a lump. firm – when moist, crushed under moderate pressure between thumb and forefinger, but resistance is distinctly noticeable. Wet soil: plastic – when wet, readily deformed by moderate pressure but can be pressed into a lump will form a wire when rolled between thumb and forefinger. sticky – when wet, adheres to other material and tends to stretch and pull apart rather than to pull free from other material. Dry soil: soft – when dry, breaks into powder or individual grains under very slight pressure. hard – when dry, moderately resistant to pressure can be broken with difficulty between thumb and forefinger. Chapter 8 151 Soil  oi ofi e oi ofi e is the vertical display of soil layers. Each layer in the soil profile is known as the horizon. It has four layers of mineral materials. The layers of soil are horizons O, A, B, C and R. Horizon O is at the very top of the profile. Horizon O is primarily composed of organic matter lying on the surface of the ground. It is usually dark in color due to the presence of organic matter. The decomposed organic matter, or humus, enriches the soil with minerals, aids soil structure (acts to bind particles) and enhances soil moisture retention. Horizon A refers to the soil beneath horizon O. It is commonly known as topsoil. It marks the beginning of the true mineral soil. In this horizon, organic material mixes with inorganic products of weathering. Horizon A typically is dark in color. Plant roots, bacteria, fungi and small animals are abundant here, and plants thrive in it. It is generally the most productive layer of soil. Horizon B is the layer below horizon A. It is known as subsoil.. Horizon B does contain some elements from horizon A because of the process of leaching. Leaching is the removal of minerals that have dissolved in the water. This horizon is usually light colored, dense and low in organic matter. Horizon C is below horizon B. Horizon C represents the weathering parent material of the soil. The upper layers are developed from this layer. Most plant roots do not penetrate this layer. Very little organic material is found here. Horizon R is the bedrock. Horizon R represents the layer hard, consolidated bedrock at the base of the soil profile. nlike the above layers, horizon R largely comprises masses of hard rock. orizon orizon orizon orizon Leaching resembles what happens in a coffee pot as the hot water drips through the grounded coffee orizon beans.   Soil profiles look different in different areas of the world as they are affected by their climate. 152 Science Focus Smart MATHAYOM 2  Q1. What is soil made up of? Q2. Name the four properties of soil. Q3. What is ? 8.1 8.2 Soil Formation Soil is a product of climate, organisms and topography acting on parent material over a period of time. The five factors that affect the formation of soils are: Parent material (texture, structure, chemical and rock composition) Climate (temperature and rain) Topography Biotic (plants and animals) Time Visit this website to The formation of soil happens over a very long period of time. It can know more in detail about the factors of take 1,000 years or more. Soil is formed from the weathering of rocks soil formation. and minerals. Weathering breaks down the rocks into smaller pieces. Slowly plants start to grow and attract small animals. These add organic matter such as leaves, twigs, and dead insects and worms. Then, the soil begins to form. Later, larger plants and animals will move in, adding more organic matter. Over years, a complex mixture of inorganic and organic materials is produced, making up the soil. A Rocks on the surface B As rocks weather into begin to fracture and smaller fragments, plants break down. begin to grow in the weathered rocks. Chapter 8 153 Soil  C Worms, insects, bacteria D When plants and animals and fungi living among the in the soil die, they break plant roots add organic down, or decay, and form matter to the soil. dark humus. It takes a minimum of 500 years to produce an inch of topsoil. Earthworms enrich topsoil with the waste they create as they eat the dead plants and animals. They also dig tunnels, loosening the soil for water and roots.   Q1. How is soil formed? Q2. How do living things speed up the formation of soil? 8.2 8.3 Soil Uses and Soil Improvement The soil is an important resource. Soil provides a medium for plants to grow, supporting the roots and supplying water, oxygen and nutrients needed for their healthy growth. The minerals in the soil are the critical components in mining. We use a lot of metal and petroleum products in our everyday life. The soil serves as the main foundation in construction and road building.    154 Science Focus Smart MATHAYOM 2  Soil absorbs rainwater and releases it later, reducing flash floods and droughts. It acts as a filter too. Rainwater goes through many layers of soil, filtering out oil, sediments and non-dissolved substances from it before becoming groundwater.    Soil serves as a habitat for many organisms. Some organisms such as worms, bacteria, insects and small mammals live in the soil. On top of the soil, a large variety of plants and larger animals live there. We use soil in pottery, ceramic-making and sculpting. Soil may lose its quality and productivity due to human activities and natural factors. It happens when the soil is deprived of its nutrients, Horticulturists are people making it less fertile and useless. When the soil is bare, it is open to who work with plants and wind and water erosion. soil. They give advices on how to improve soil, Soil improvement is the process of making the following aspects of analyze and develop soil favorable for plant growth. They are soil structure, soil drainage solutions in farms and forests. and water holding capacity, as well as its nutrient holding capacity and availability. This is because the physical and chemical properties of soil change over time, and the kinds of plants we grow and how we grow them may also affect our soil improvement practices. More organic matter in the soil improves soil structure, filtration, drainage, and water and nutrient holding capacity. It makes the soil fertile, resulting a favorable rooting environment for plants. Soil organic matter also serves as a source of food and energy for a myriad of beneficial microorganisms. Natural or synthetic fertilizers contain plant essential elements aimed at improving soil to promote plant growth. Improper use of fertilizers A compost pile contains a variety of microorganisms can cause harm to the environment and damage to plants. that help to break down materials within the Soil pH affects the solubility of nutrient elements required by plants. compost. It allows us to In general, plant essential nutrients are most available around the turn organic matters into slightly acidic to near neutral soil pH values of 6.0 to 6.8. something useful. We can save the landfill space and However, there are some exceptions. Iron, which is required in improve the soil condition at the same time. relatively high amounts, is more available at lower soil pH values. Also, both high and low soil pH values decrease the availability of phosphorus. An undesirable soil pH value can limit plant growth as it affects nutrient availability, plant physiological functions and soil microbe activities. Chapter 8 155 Soil  Modifying soil pH values Test the soil first. If a soil test indicates the soil pH value is not in the optimal range for growing plants, pH modification may be necessary. Typically, ground limestone is used to raise soil pH value while sulfur or sulfur compounds are used to lower it. How much to apply depends on the present soil pH value, the desired pH change, and the amount of clay and organic matter present in the soil. Nutrient disorders can affect the look or health of plants by disrupting internal plant mechanisms that cause the plant to not function properly. It may be noticed as nutrient toxicity, when too much of a nutrient is available, or nutrient deficiency when not enough of a nutrient is available to the plant. Both can lead to problems on how the plant functions and grows. If the soil has the right balance of nutrients, air, water, minerals and organic matter, the plant will have access to the nutrients it needs to function and grow properly. If the soil is not managed properly, plants are likely to compete for nutrients and resources, making them function poorly due to nutrient disorder. This can weaken the plants, making them susceptible to other problems. Both soil texture and soil structure influence the drainage capacity of a soil. Adequate soil drainage enables a plant to access to the air, water and nutrients it needs to survive and flourish. Poor soil drainage can inhibit a plant’s access to air, water and nutrients, causing stress and sometimes death. 156 Science Focus Smart MATHAYOM 2  Q1. Name three uses of soil. Q2. Give three ways to improve soil. 8.3 Soil consistency Soil structure Soil texture Soil color Soil properties Components oi ofi e Horizons Soil Soil improvement Uses methods Medium for plant Adding organic growth matter Absorbs rainwater Adding fertilizers Improving pH As water filter values Balancing As a habitat nutrients Having adequate For pottery soil drainage Chapter 8 157 Soil  Fill in the blanks with the given words. soil texture fertility horizon A soil profile absorbing horizon O supports smaller habitat horizon B soil consistency soil peds larger soil metals weathering 1. is the mixture of organic matter, inorganic matter, air, water and soil organisms. 2. determines the amount of water retained by the soil and the air movement. 3. Sandy soil has pores. This makes the soil retain less water and has better air movement. 4. Clay soil has pores. This makes the soil retain more water and has poor air movement. 5. are the basic units of soil structure. 6. refers to the ease of a soil ped that can be crushed by fingers. It also depends on the moisture content. 7. is the vertical section of the horizons of soil. sually, there are five horizons – horizon O, horizon A, horizon B,horizon C and horizon R. 8. is the very top part that has decomposed organic matter. 9. is below horizon O, which is known as top soil. It is rich in organic matter and dark in color. 10. is below horizon A and contains some elements from horizon A. 11. Soil is formed due to the of rocks and minerals. 12. Soil is an important resource. It the plants and supplies nutrients to the plants. 13. Soil contains minerals such as and petroleum which can be used to make things. 14. Soil prevents floods and droughts by rainwater and releasing it later. 15. Soil is the for many living things. 16. Soil will lose its and usefulness due to human and natural factors. 158 Science Focus Smart MATHAYOM 2 1. (a) What is soil made up of? (b) Name three types of soil. (c) Which of the three types of soil is most suitable for the garden? 2. (a) What is a ? (b) Draw a labeled diagram of a soil profile. (c) Which layer in a soil profile contains the most organic matter? (d) Which layer contains mainly the unweathered bedrock? Chapter 8 161 Soil