explain the properties of soil
Answers
Answer:
Soil texture
Soil is made up of different-sized particles. Soil texture refers to the size of the particles that make up the soil and depends on the proportion of sand, silt and clay-sized particles and organic matter in the soil. Sandy soils feel gritty when rubbed between your fingers. Silts feel smooth – a little like flour. Most clays are sticky and mouldable. If you’ve ever used pottery clay, you’ll know the feeling.
Soils are made up of different combinations of sand, silt and clay particles. Soils that are a mixture of sand, silt and clay are called loams. The name of the soil often identifies the dominant particle, for example, Timaru silt loam describes a soil that has a predominance of silt. Other examples of New Zealand soils are Waikare clay and Te Kopuru sand.
Soil formation
Professor Louis Schipper from Waikato University briefly explains the five factors involved in soil formation.
Soil texture can influence whether soils are free draining, whether they hold water and how easy it is for plant roots to grow.
Sand particles are quite big. The pore spaces between the particles in sandy soils are also quite large. This allows water to drain quickly and air to enter the soil. Sandy soils tend not to get waterlogged in winter but can be subject to drought during summer.
Silt particles are too small for us to see with our eyes. Silt soils have much smaller pore spaces but a lot more of them.
Clay particles are smaller than 0.002 mm in diameter. Clay soils are poorly drained and hold on to the water in their pore spaces for much longer. However, they can become very hard if they dry out.
Soil structure
Soil structure describes the way the sand, silt and clay particles are clumped together. Organic matter (decaying plants and animals) and soil organisms like earthworms and bacteria influence soil structure. Clays, organic matter and materials excreted by soil organisms bind the soil particles together to form aggregates. Soil structure is important for plant growth, regulating the movement of air and water, influencing root development and affecting nutrient availability. Good quality soils are friable (crumbly) and have fine aggregates so the soil breaks up easily if you squeeze it. Poor soil structure has coarse, very firm clods or no structure at all.
Soil porosity
Important soil properties
Professor Louis Schipper talks about the importance of soil structure, soil chemistry and soil organic matter.
Soil porosity refers to the pores within the soil. Porosity influences the movement of air and water. Healthy soils have many pores between and within the aggregates. Poor quality soils have few visible pores, cracks or holes. The way in which a soil is managed can affect its porosity. For example, look at areas around your school where students regularly walk. If the grass is worn away and the soil is exposed, it often looks different because it has been compacted and has had its structure and porosity altered. These are also areas where puddles form because the water is not able to drain away.
Soil chemistry
Clays and organic matter in the soil carry negative charges. Water in the soil dissolves nutrients and other chemicals. Nutrients like potassium and ammonium have positive charges. They are attracted to the negatively charged organic and mineral matter, and this prevents them from being lost through leaching as water moves through the soil. Nitrate has a negative charge so it is not protected from leaching in most soils.
Soils can be acid, alkaline or neutral. Soil pH influences nutrient absorption and plant growth. Some plants, like kūmara and potatoes, grow best in a more acidic soil (pH of 5.0–6.0). Carrots and lettuces prefer soils with a neutral pH of 7.0. Soils can become more acidic over time as minerals are leached away. Lime is often added to soil to make it less acidic. New Zealand paddocks are regularly limed to improve pasture growth.
Soil colour
If you thought that all soils are brown, think again. Soil colours range from black to red to white. Sometimes it can even be blue! Soil colour mostly comes from organic matter and iron. Topsoil is often dark because of organic matter. An even, single colour indicates the soil is well drained. In contrast, rusty spots and grey patches (sometimes even a light blue in colour) indicate poor drainage.

Soils are not all the same
Soils can differ widely from location to location. Soil colour depends on organic matter and mineral content and is influenced by drainage. These soils are Te Rapa peaty, Bruntwood silt loam and Egmont black loam.
Explanation:
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Answer:
Physical Properties of soil
1. Soil texture:
Soil texture defines the proportion in which the soil separates to make the mineral component of the soil. These separates can be classified as sand, clay, and silt. Sand and silt are of no importance to the soil as they don’t contribute to the soil’s ability to restore water or nutrients. Clay is an active part of soil texture as clay has a small size and it has a large amount of surface area per unit mass and it helps in storing ions and water.
2. Soil Color
Basically soil color (brown, yellow, red) depends on oxidized or ferric iron compounds. Darker the color of the soil, the more organic content it contains. The higher the organic content, higher soil temperature as they absorb more heat due to the darker color.
3. Soil Horizon:
The soil is divided vertically into different horizons from top to bottom namely:
A-Horizon: This is the uppermost layer of soil and also called as topsoil. This layer is rich in humus and minerals and holds most of the water as compared to other layers. This layer consists of sand, silt, and clay. It is also a home to many living organisms like snakes, earthworms, etc.
B-Horizon: This is the second layer from the top and is little rich in humus and it supports moisture. This layer consists of silt, clay, weathered rocks and some nutrients. Minerals are more in this layer as compared to the top layer.
C-Horizon: This layer consists of small pieces of rocks broken down due to weathering.
Bed Rock: This layer is the last layer and consists of layers of solid unweathered rock.
Chemical Properties
1. Inorganic matters of soil
From the accounts given in the description of weathering process it is clear that compounds of aluminium, silicon, calcium, magnesium, iron, potassium and sodium are chief inorganic constituents of soils. Besides these, the soils also contain small quantities of several other inorganic compounds, such as those of boron, magnesium, copper, zinc, molybdenum, cobalt, iodine, fluorine etc. The amounts of these chemicals vary in soils of different places. Chemical composition of soil of one horizon differs greatly from the composition of soil in the other horizon.
2. Organic Matters in Soil:
Organic component of the soil consists of substances of organic origin; living and dead. In sandy soil of arid zone, it is found in very poor quantity (one or less than one per cent) but in peaty soil, it may be as high as 90%. When the plants and animals die, their dead remains are subjected to decomposition.
As a result of decomposition a number of different organic products or compounds are formed from the original residues. In the course of decomposition, the original materials are converted into dark coloured organic complexes, called humus. Sometimes living micro-organisms add sufficient amount of organic matters in soil in the form of metabolic wastes.
Chemists have been attempting to unravel the details of humus composition since the earliest days of soil science, and have got much success but more is yet to be discovered. In terms of specific elements, the organic component of soil contains compounds of carbon, hydrogen, oxygen, phosphorus, nitrogen, sulphur and small amount of other elements also. Only small fraction of total organic matter is soluble in water but majority of them are soluble in alkali solution.
3. Colloidal Properties of Soil Particles:
There are two types of substances namely crystalloids and colloids:
Crystalloids are those crystalline solid substances which form true solution on being mixed with other substances. In true solution, crystal particles cannot be seen with the help of microscope.
The word colloid first coined by Grahm (1849) is derived from Greek words kolla meaning glue and eoids meaning appearance, i.e., glue like in appearance. Colloid is really speaking amorphous state of the substances which do not form true solution if mixed with other substances. The particles of colloidal substances float in the solvent in suspension state but do not tend to settle at the bottom. Colloids are not found in ionic or molecular form but are found in aggregates of atoms or molecules.
Colloidal system or suspension contains two phases which are:
(i) Dispersion phase, i.e., medium in which the particles are suspended, and
(ii) Dispersed phase, i.e., suspended particles.
Colloidal suspension may be of different kinds, such as:
(1) Suspension of liquid, in liquid, as milk (fats in water).
(2) Suspension of solid in liquid as India ink (or clay suspension in water).
(3) Suspension of solid in gas, as smoke (coal particles suspended in air).
(4) Suspension of liquid in gas, e.g., cloud and fogs in atmosphere.
ical properties of soil.