Soil Science

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• Soil is a material composed of five ingredients:

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• minerals

• water

• air

• organic matter

• microbial life

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what are the other functions of soil?

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-Habitat for soil organism

-Water supply and purification

-Engineering medium

-Recycling nutrients and organic wastes

-Meduim for plant growth

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Is the study of soil as a natural resource on the surface of the Earth including soil formation,classification and mapping; physical, chemical,biological, and fertility properties of soils

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Soil science

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Deals with the systematic study of soils as a non-renewable (or very slowly renewable)resource that should be carefully managed so that itcould serve our generation and future generations.

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Soil science

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Fundamental to land evaluation or land use planning.

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Soil survey

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Usually investigate the biological, chemical, physical and mineralogical properties of soils which are then grounded and classified.

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Soil Scientists

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Composition of Soil

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- Mineral

- Orgamic Matter

- Air

- Water

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Soil genesis or pedogenesis, from the Greek word:

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- pedon means soil - genesis means origin or birth.

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Is the process of soil formation or study of the origin and formation of soil.

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Soil genesis

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Is the starting material of soils. A rock is defined as a consolidated mass composed of one or more minerals. A set of processes and factors act on rock to produce soil.

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Parent rock

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Rocks are residual or in-place parent material that weathers into soilwithout first being moved by wind or water.

• Rocks are divided into three main groups?

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-igneous

-sedimentary

-metamorphic

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It form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust.

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Igneous rocks

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2 types of Igneous rocks

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-intrusive

-extrusive

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Rocks form inside the Earth from magma.

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INTRUSIVE: Intrusive (or plutonic) rocks

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(For example, gabbro, granite, and pegmatite rocks)

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Rocks cool and solidify on the surface.

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EXTRUSIVE: Extrusive rocks

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(For example, basalt, andesite, and obsidian.)

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Exmples of INTRUSIVE rocks

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-pegmatite

-gabbro

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Example of EXTRUSIVE rocks

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-basalt

-andesite

-obsidian

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formed on or near the Earth’s surface, in contrast to metamorphic and igneous rocks, which are formed deep within the Earth and compacted under high pressure.

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Sedimentary rocks

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geological processes that lead to thecreation of sedimentary rocks

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-erosion

-deposition

-compaction

-cementation.

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These sediments are carried away by wind and water. • As they carried away they are broken down more.

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erosion

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• Eventually those carried away sediments will be deposited when sediments settle out of moving currents

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deposition

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When streams enters the lake When river enters the ocean

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• Sediments build up, it will compact. • Pressure from the layers above push down on the lower layer.

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compaction

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Tightly pack sediments

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Cementations

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began as a rock—either a sedimentary, igneous, or even a different sort of metamorphic rock.

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metamorphic rock

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Then, due to various conditions within the Earth, the existing rock was changed into a new kind.

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Cooling of magma

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Igneous rocks

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Deposition and compaction

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Sedimentary rocks

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Change in igneous and sedimentary

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Metamorphic rocks

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Example of sedimentary

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-Shale

-Sandstone

-limestone

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Examples of metamophic rocks

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-slate

-marble

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• He developed soil science in Russia, and was perhaps the first person to conduct broad geographical investigations of different soil types.

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Vasily Vasilevich Dokuchaev

Father of Soil Science

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First person to show soils usually pattern in the landscape and established that they develop as a result of the interplay of soil-forming factors.

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coined the term “pedogenesis”, which is the process of soil formation, and formulated this concept into the now famous “fundamental equation of soil-forming factors” or Jenny Equation: s = f (cl, o, r, p, t, …)

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Hans Jenny

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Classification of soil forming factors:

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-Passive Factors - Active Factors

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Passive Factors:

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• Parent Material • Relief or Topography • Time

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Active Factors:

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• Climate • living Organisms

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The soils will carry the characteristics of its parent material such as:

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-color

-texture

-structure

-mineral composition.

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Soil parent materials represent the initial state of the soil system. There are essentially 2 types of original parent material:

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• Residual Parent Material • Transport Parent Material

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developed in place (in situ) from the underlying rock. Typically it experienced long and intense weathering. Residual parent materials can be found overlying any rock type – provided that the landscape has been stable for a sufficient period of time for weathering to occur.

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Residual or sedentary

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loose sediments or surficial materials (i.e., weatheringproducts of rocks that are not cemented or consolidated) that have been transported and deposited by gravity, water, ice, or wind. These materials areclassified on the basis of the agents responsible for their movement anddeposition.

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Transported parent matetial

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• Topography or relief is commonly considered to be a factor that modifies the effects of other factors of soil formation such as established before soil formation begins. • Material will be forced into valleys by gravity. Valley soils will therefore be deeper and richer with organic matter and soils on slopes or at higher altitudes tend to be poorer and thinner.

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relief or topography

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• The amount of time a soil requires to develop varies widely according to the action of the other soil-forming factors.

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time

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• Amongst all the soil forming factors, climate is perhaps the most influential in soil development. • Precipitation and temperature are the two major climate elements which contribute most soil formation.

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climate

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• Vegetation and organisms play a critical and interconnected role in soil formation, influencing the development and characteristics of soils in various ways.

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organisms & vegetation

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Tranforted parents material

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-relief or topography

-time

-climate

-organisms & vegetation

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:Vegetation, including trees, shrubs, grasses, and other plants, contributes organic matter to the soil through leaf litter, fallen branches, and plant roots.

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Organic Matter Input

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• Microorganisms, including bacteria and fungi, decompose organic matter from vegetation, breaking it down into humus.

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Decomposition

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• Soil organisms play a significant role in nutrient cycling.

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Nutrient Cycling

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• Plant roots and soil organisms produce organic compounds that bind soil particles together into aggregates.

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Soil Aggregation

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• Soil organisms, including earthworms, nematodes, and bacteria, participate in various biological processes that influence soil properties. organisms & vegetation

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Biological Activity

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The weathering processes

There are two main processes that lead to the formation of soil:

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• Physical weathering

• Chemical weathering

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which does not involve chemical change.

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• Physical weathering

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involves chemical changes.

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• Chemical weathering

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is the breaking of rocks into smaller pieces. This can happen through exfoliation, freeze-thaw cycles, abrasion, root expansion, and wet-dry cycles.

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Physical weathering

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4 PHYSICAL WEATHERING process

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-Exfoliation

-Freeze-thaw

-Abrasion

-Root Expansion

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When temperature of rocks rapidly changes that can expand or crack rocks.

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Exfoliation

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: When water freezes, it expands. If moisture seeps into cracks before winter, it can then freeze, driving the rocks apart.

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Freeze-thaw

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: When the wind blows, it can pick up sand and silt, and literally sandblast rocks into pieces.

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Abrasion

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: Like freeze thaw, roots grow bigger every year. These roots can drive the roots apart.

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Root Expansion

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Major chemical reactions include carbonation, dissolution, hydration, hydrolysis, and oxidation- reduction reaction. All of these reactions have water involved with them.

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CHEMICAL WEATHERING

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4 process of chemical weathering

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-Carbonation

-Dissolution/Leaching:

-Hydrolysis

-Oxidation

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is a common form of a chemical reaction where water is mostly used to break down the chemical bonds that exists between a particular substance.

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Hydrolysis

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Minerals in the rock react with water and surrounding acids. The hydrogen atoms replace other cations. Feldspar hydrate to clay.

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: When water reacts with carbon dioxide, it creates carbonic acid, which can dissolve softer rocks.

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Carbonation

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• process that occurs when carbon dioxide (CO2) from the atmosphere or other sources reacts with minerals in rocks, particularly carbonate minerals like limestone (calcium carbonate) and dolomite (calcium magnesium carbonate). This reaction leads to the breakdown of these minerals and the eventual alteration of the rock's composition and structure

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: Limestone and rocks high in salt dissolve when exposed to water. The water carries away the ions.

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Dissolution/Leaching

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Physical characteristics of soil

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• Color • texture • aggregation • porosity • ion content • pH

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Charts that helps to identify the soil color

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munsel color chart

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Soils come in a wide range of colors – shades of brown, red, orange, yellow, gray, and even blue or green.

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Color

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Soils with significant organic material content appear dark brown or black. The most common soil hues are in the red-to-yellow range, getting their color from iron oxide minerals coating soil particles. Red ion oxides dominate highly weathered soils. Soils frequently saturated by water appear gray, blue,or green because the minerals that give them the red and yellow colors have been leached away.

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refers to the relative proportions of sand, silt, and clay particles in the soil. It is a fundamental physical characteristic that influences soil properties such as water-holding capacity, drainage, aeration, and nutrient retention. Soils can be classified as sandy, silty, clayey, or loamy, depending on their texture.

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texture

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refers to the arrangement and aggregation of soil particles into clusters or aggregates. Well-aggregated soils have good soil structure, which provides space for air and water movement, root penetration, and microbial activity. Soil structure can be granular, blocky, prismatic, or platy, among others.

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aggregation

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Cation Exchange Capacity (CEC) measures the soil's ability to retain and exchange essential nutrients, particularly cations (positively charged ions like calcium, potassium, and magnesium). Soils with higher CEC can retain more nutrients and make them available to plants. CEC is related to soil colloids and organic matter content. Ion Content(CEC)

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Ion Content(CEC)

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the volume of open spaces (pores) in the soil. Porosity influences the movement of air, water, and roots through the soil. Sandy soils have larger pores, which result in higher permeability but lower water-holding capacity, while clayey soils have smaller pores, leading to lower permeability but greater water retention.

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porosity

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Soil pH measures the acidity or alkalinity of the soil. It is a critical factor that affects nutrient availability and microbial activity. Soils can be acidic (pH < 7), neutral (pH = 7), or alkaline (pH > 7). Different plants thrive at different pH levels, and soil pH can be adjusted through soil amendments.

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Ph

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The different layers of soil are:

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• Topsoil • Subsoil • Parent rock

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is composed of a series of horizons or layersof soil stacked one on top of the other. These layers orhorizons are represented by letters O, A, E, C, B and R.

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soil profile

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SOIL PROFILE

Soil horizon

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