Soil Science Review Flashcards

Flashcards based on lecture notes covering soil science, including definitions, soil physics, soil chemistry, and soil management.

What is soil security?

The maintenance and improvement of global soil resources to produce food, fibre and fresh water, contribute to energy and climate sustainability, and to maintain the biodiversity and the overall protection of the ecosystem

Define soil.

The unconsolidated cover on the surface of the earth.

What is soil physics?

The study of soil physical properties and processes - solid, liquid, gas.

What does soil texture refer to?

The size of individual particles.

What is soil consistence?

The strength with which soil materials are held together and the resistance of the soil to deform or rupture. It varies with moisture content.

What is soil structure?

The arrangement of the primary soil particles and other materials into discrete aggregates.

What is slaking?

The breakdown of large, air dry soil aggregates into smaller aggregates when immersed in water e-g internal stress

What is soil porosity?

The pore space in the soil between the mineral and other particles like organic matter that are filled with either air or water.

Define Bulk Density.

Mass of dry soil per unit volume of whole soil-particles and pores included

Define Particle Density.

The mass per unit volume of the solid portion of the soil

What is soil compaction?

When soil particles are pressed together reducing pore space between them

Define Minerals.

Naturally occurring inorganic elements of compounds that have a characteristic chemical composition and structure

What are Rocks?

Aggregates of minerals and other undifferentiated matter

What does landscape refer to in soil science?

The area of land being examined that includes the surface features, as well as the deeper layers beneath it, such as the type of rocks and soils present. It represents the full combination of natural elements that shape and influence that piece of land.

What are the factors of soil formation (CORPT)?

Climate, Organisms, Relief, Parent Material, Time

List the different types of soil texture.

Sand, Silt, Clay, Gravel

How are soil aggregates formed?

Through physical, chemical and biological activity below ground

Why is soil aggregate stability important?

Impacts water holding capacity, nutrient supply + compaction, key indicator of soil quality, Impacts soil pore size distribution, Affects soil aeration

What impacts soil structure?

Tilling soils that are too wet, compacting soils with heavy machinery + livestock, Vegetation removal, Freeze/than + wet/dry cycles

Define Macropores.

Large pores that drain quickly. When the pores are full the Soil is waterlogged. Can be caused by soil cracking, aggregation, plant roofs and soil Macrofauna.

Define Mesopores.

Medium sized pores that hold most of the plant available water. Consist of both air and moisture. The more mesopores the greater the water holding capacity of the soil.

Define Micropores.

Smallest pores. Water held here only available to microbes

What is Bulk Density used for?

Convert measurements of gravimetric water to volumetric water, Calculate soil properties per unit area, Indication of soil compaction.

Explain Soil Compaction/weight.

Natural Compaction can be caused by Raindrop impact, Soil weight, Induced Compaction can be caused by Livestock, Machinery.

What are the two types of forces in the water cycle?

Cohesive and Adhesive forces. Cohesive are the forces between water molecules, while adhesive forces are between water molecules and other substances.

What is Matrix Force?

The combination of cohesive and adhesive forces. Further away from the soil particle the water becomes the more available it is to the plants.

What is capillary rise?

The movement of water in narrow spaces without the aid of external forces

What is soil water potential?

The work necessary to transfer water from a specified elevation and pressure to another point somewhere in the porous medium. Lower potential water will stay in one place white a high potential water will move around freely.

List the different types of Soil Water Levels.

Wilting Point- unavailable to plants. Stress Point- little water available to plant. Field Capacity- good for plants as there is both water and oxygen available. Full Saturation- no oxygen in soil.

What is Hydraulic Conductivity?

The ease with which water moves through the soil

What is infiltration?

What is Porosity?

What is Permeability?

Process by which water on the ground surface enters the soil.

Amount of pores in the soil

The way the soil is structured it doesn’t let the water through, there is only adhesive forces.

What are Wetting Fronts?

The boundary or interface between a soil that is dry and a soil that is newly wetted, characterized by a sharp change in water content and often a visual change in colour as water infiltrates

Where do plants access water from?

Plants access water via root hair, if it is humid the plant wont need to extract water from the soil

Define Point Source Pollution.

In a particular area, identity is known

Define Diffuse Source Pollution.

Spread over wide area, source not always easily identified

How do hydrocarbons effect the soil?

Reduce porosity, decrease soil water infiltration and retention due to their hydrophobic nature

What causes Water Repellence?

A waxy coating building up on soil particles and hydrophobic particulate organic matter, which usually occurs in the topsoil with low clay content

List the managing water repellence strategies.

Furrow sowing, No till, Decaying crop residues and roots leave channels for water to infiltrate soil, Seeding without disturbance with stubble retention allows for soil macro-porosity to be preserved allowing for water infiltration, Spading, Clay delving, Invert non-wetting layer to depth, Clay spreading, Wetting agents

What is and causes water logging?

Occurs when soil is so wet there is insufficient air in spore spaces for roots to respire.

Surface seal, Hard setting layer, Compaction, Impermeable subsoils

List what happens to the crop during water logging.

O2 decreases (respiration starts), CO2 increases (respiration by product), Ethylene increases (stress response), O2 disappears (plant metabolism increases), Nitrate disappears (due to m=low metabolism driving N uptake resulting in chlorosis symptoms), hydrogen sulphide appears (toxic to plants), Methane appears

List the managing water logging strategies.

Deep drains- control water table, Raised Beds- improve drainage and root aeration.

Define Water Erosion.

Occurs when the soil is removed by rain, runoff, snow/ice melt or irrigation and is impacted by soil texture, structure, vegetation cover and topography.

List the different types of water erosion.

Sheet erosion, rill erosion , Gully erosion tunnel erosion and sink holes

Why should you care about soil pH?

As there is different nutrients in the soil at different pH levels, Aluminium levels decrease with pH decreasing its toxicity, Ribosomes in soil decreases with acidity affecting number of nodules on plants to capture nitrogen

List the different causes of soil Acidification.

Parent material- granite more acidic then limestone

Acid Rain- nitrogen and sulphate released into atmosphere

Leaching- Base cations leached and acid cations build up.

Hydrogen Build Up- Aluminium forms bonds with water causing hydrogen to become free in soil

List the effect of soil pH on plant nutrients.

Alkaline =Calcium and Magnesium deficiency and low levels of Phosphorous

Acidic- major nutrient deficiencies of nitrogen, potassium and sulfur and toxic levels of aluminium

List the different causes of soil Alkalinity.

Parent material- Calcium carbonate rich limestone

Loss of topsoil- Exposes alkaline subsoil

Poor drainage- accumulation of soluble salts like Na

Irrigation water containing high levels of bicarbonates

Mining- disposing of alkaline bauxite residues

Over-liming

How does Alkalinity Effects Plant Nutrients.

Phosphorus deficiency, Iron deficiency, Copper and Zinc deficiency

Why is it important to sample subsoil?

Testing topsoil pH only tells you about the topsoil pH, Extra lime is required to treat the acidic subsurface layer from about 10-40cm, The acidic layer prevents roots from growing into the good soil below 40cm

What are the different sources of lime and how does it work?

Lime sand, limestone, dolomitic lime, on farm lime sources- Morrell soil

It bonds with hydrogen decreasing the amount of free hydrogen in the soil reducing soil acidity

List the different ways to manage Alkaline soils.

Improve drainage- reduce salt accumulation

Soil Organic Matter- improves soil structure and can release hydrogen from binding sites in high pH soils.

What is Soil Salinity and what common salts?

Refers to the amount of salt in the soil. Salts most commonly present are chlorides and sulphites of sodium, calcium and magnesium, nitrates may also be present

Where does salt in the landscape come from?

Wind borne, Pollution dissolved in rainwater, Fossil salt in marine sediments, Weathering of parent rock

What is Primary Salinity?

Natural Salinity- Rainfall insufficient to leach salts

What is Secondary Salinity?

Irrigation -rises groundwater tables -use of poor quality water adding calcium and sodium increasing salinity

List the effect of Salinity on Plants and Soils.

Poor plant growth first indication and salinisation, Tomic ions like sodium and chloride, ionic imbalance, Water logging increases negative effects, Soil sodicity

How to Manage Saline soils?

Plant based options - salt bushes

Revegetation- agroforestry

Engineering- surface water management by increasing discharge

No Active Management- allow natural revegetation

What is Soil Sodicity?

There is high levels of exchangeable sodium which dominates other cations, Soil becomes dispersive and structure collapses

What are the impacts of sodic soils on farm production?

Surface crusting, Reduced seeding emergence, Reduced soil aeration, Increased run-off and erosion risk, Less ground cover and organic matter, Less microbial activity

How to Measure and Manage Sodic soils?

Doing a dispersion test .

Add gypsum which decreases ESP, calcium, displaces sodium on soil surface and only add lime to acid soils, Organic matter , Deep ripping

Why do colloids matter?

When it rains water flows through soil but nutrients don’t always leaves because of tiny, charged particles called colloids which act like magnetic sponges, holding nutrients in place for plants.

What are Colloids?

Very tiny particles smaller than bacteria which stay suspended in water which have an electric charge and very large surface area which makes them the most chemically active part of the soil holding soil nutrients

List the different broad types of colloids.

Clay colloids- platy and layered, permanent charge

Metal oxide- round coated particles, pH dependent charge

Organic colloids- humus, non crystalline, pH dependent charge

What is Cation Exchange Capacity (CEC)?

Soils ability to hold and exchange positively charged ions (cations) on colloid surfaces

How do plants use CEC?

Plant roots released hydrogen ions directly or via CO2 from respiration, These hydrogen ions displace the nutrient cations from the colloids surface, The freed-up nutrient cation enters the soil water (soil solution), They can then be absorbed by the plant roots

List what influences CEC.

Texture- more clay higher CEC

Mineralogy - Kaolinite = low CEC 1:1 structure, Smectite= high CEC 2:1 structure Organic Matter- Extremely high CEC

pH- higher pH equals more negative charges allowing for a higher CEC

What is the importance of soil organic matter?

Plays a crucial role in soil health, Improves biological, physical and chemical properties of soil. A source of nutrients, increase water retention and supports soil organisms.

List the Essential Plant Nutrients.

Organic Nutrients - Carbon, Hydrogen, Oxygen

Macronutrients (>1000mg/kg) - Nitrogen, Potassium, Calcium, Phosphorus, Magnesium, Sulphur

Micronutrients (<1000mg/kg) -Iron, Chlorine, Boron, Manganese, Zinc, Copper, Molybdenum, Nickel

Where do elements in soil come from?

Plant symbiosis of nutrients from nitrogen fixing bacteria, Parasitism , Fertilisers, Parent material, Decomposition

Nitrogen Cycle

Nitrogen fixation where atmospheric nitrogen is converted into ammonium by bacteria or lightening. Through nitrification, the ammonia is turned into nitrates which the plants absorb. Animals can obtain nitrogen by consuming plant materials. When they die to release waste ammonification breaks it down into ammonia. Denitrification returns nitrogen into the atmosphere by bacteria converting nitrates back into atmospheric nitrogen.

What is Ammonia Volatilisation and Factors Affecting it.

When urea fertilisers are applied to soil and not properly incorporated where it breaks down into ammonia which can evaporate decreasing nitrogen available to plants

pH, Temperature, Wind , Moisture, Soil structure, Low CEC

What is Biological Nitrogen Fixation?

Where rhizobia form a symbiotic relationship (nodules) on roots which convert nitrogen gas into ammonia for plants to use

Define Potassium, impacts, movement and deficiency symptoms.

Second most consumed nutrient which impacts stomatal regulation, water uptake and loss. It diffuses form high concentration to low concentration. Canola- interveinal yellowing and bulging veins. Wheat- paler, weak more susceptible to disease

Define Phosphorus, impacts, movement and deficiency symptoms.

Most Wa soils are very low in P. Added into soil via fertilisers, plant residues and agricultural wastes. Low absorption capacity and easily leached and not readily availble to plants as it binds tightly to soil. Darkened reddish purple leave tips

Define Sulphur, movement, deficiency symptoms.

Derived from sulphate minerals like gypsum and atmosphere. Sulphate anion used by plants. limited mobility in plants but mobile in soil. Plants grow poorly, reduced tillering, yellowing of younger leaves.

Why is calcium important to plants and calcium deficiency.

Component of cell walls and membranes, Roles in protein formation and carbohydrate movement, Poor movement in plants. Tips look burnt and tissue breakdown.

Why is magnesium important to plants and magnesium deficiency.

Core of chlorophyll, Essential for photosynthesis. Interveinal chlorosis- yellowing

List the characteristics of a healthy soil.

Soil Biodiversity, Plant Diversity, Local Soil Type , Land Management

Describe Soil Biodiversity.

Nutrient transformation

Nutrient Cycling

Symbiotic/ non-symbiotic nitrogen fixation- interaction between plants and mycorrhizal

Plant disease / plant disease suppression

Soil structure- bacteria and fungi help to form soil aggregates- hyphae

Water repellence/ infiltration- some cause waxes and others break it down

What are silicate minerals?

Silicate tetrahedron made up of 3 oxygen and 1 silicone atom causing it to have a negative 4 charge making it quite reactive

Discuss texture contrast soils.

Where there is a sharp boundary between one layer and the next. The boundary is very distinct to see and the texture will be very different

How Does Soil Vary in a Global Scale?

Particle and pedon scale, Paddock size field map, Continental map, How soil varies in a global scale

What is spatial soil variability?

Spatial prediction can be made on the basis of the similarity of landscape between a sample and a prediction point - where we actually sample a point and where we are going to use that to predict a point where you cant sample

What is the Deterministic Component?

Represented by a general mean - Considered soil as a natural body with its own genesis and development, postulating that bedrock becomes soil under the combined influence of give soil formation factors including climate, organisms, parent material, time and relief

What is Open Pit Mining?

The process begins by removing topsoil and vegetation from the area - Is suitable for extracting minerals that aren’t very far below the surface - Lower operating costs due to the relatively straightforward extraction process and the use of large-scale equipment resulting in lower labor and energy costs

What is Underground Mining?

Involves creating tunnels to access minerals deposits located deep beneath the earth’s surface - Enables the extraction of valuable resources that would otherwise be be inaccessible - More expensive due to the complex infrastructure required for accessing and extracting minerals from the deep underground

What are the negative effects of mining?

Soil degradation, Sinkholes, Deforestation, Water pollution, Effect on biodiversity and terrestrial organisms, Waste material

What are the Key Rehabilitation & Mines Closure Issues?

Acid and Metalliferous Drainage- natural oxidation of sulfide minerals when exposed to air and water

Dispersive Materials- tunnel erosion that can lead to gully erosion by saline sodic materials

Mine Pit Lakes- filled up with water

Radioactivity- uranium

How to Measure Plant Available Water?

Drained upper limit and the crop lower limit. This measurement determines the amount of water that plants can readily use for growth.

Pollution and Soil Water- Diffuse

Spread over wide area, source not always easily identified

What is Buffering Capacity

The ability of soil to resist changes in pH when acidic or alkaline substances are added.

How to measure soil organic carbon?

Loss of ignition- measures the mass loss of organic matter. However, it can burn things that aren’t organic matter making it overestimate.

Trace Elements and their Deficiency Impacts.

Magnesium- yellowish between veins on young leaves or brown dead spots

Copper- new leaves die back, pale weak heads in cereal

Iron- young leaves turn yellow while the veins remain green

Microbial Interaction- nitrogen cycle

When wet or dry conditions are present different organisms will be working meaning different processes will be undergone.

Ammonification- aerobic

Nitrification- between aerobic and anaerobic

Denitrification- anaerobic

Importance of plant biodiversity in soil

Growing different plants in the soil you will have different microbial communities in the soil. Diversity in microbes will equal diversity in what they do

Framework Silicates

1. Quartz

   • simplest of the framework silicates

   • glassy, clear mineral

   • stays in environment and weathers down to sand

2. Feldspars

   • most common mineral is earth crust

   • weathers down to kaolin or silica

     A) Othroclase Feldspars

   • potassium aluminium silicate

   • white-pink colour

   • found in granites

     B) Plagioclase Feldspars

   • white to grey colour

   • twinning thing straight cleavage

Sheet Silicates

1. Muscovite Mica

   • potassium aluminium silicate

   • light in colour

   • basal cleavage into thin sheets

   • rapidly turns into smectite

2. Biotite Mica

   • potassium, iron, magnesium, aluminium silicate

   • brown to black in colour

   • perfect cleavage to form sheets

   • change to clay like smectite

Chain Silicates

1. Pyroxines e.g. Augite

   • single chain ferromagnesian silicates

   • dark green to black

   • weathers down to smectite

2. Amphiboles e.g. Hornblende

   • double chain ferromagnesian silicates

   • dark green, brown to black

   • weathers down into kaolinite

Iron Oxides/ Hydroxides

1. Magnetite

   • strongly magnetic

   • metallic black with black streak

   • only found is fresh rocks

   • weathers hematite and magnetite

2. Hematite

   • the oxidised end product of magnetite

   • metallic grey

   • streak red blood

3. Goethite

   • composed of iron oxide and manganese

   • formed under oxidising conditions as a weathering product of iron minerals

   • blackish brown with red to brown yellow streaks

Aluminium Oxides

1. Gibbsite

   • minders form aluminium hydroxide

   • one of the most common minerals in bauxite

   • white and glassy but also greeny/blue, pink

   • weathering product of ferromagnesians