ESS soil unit 5

Soil

a dynamic, open system composed of minerals, organic matter, water, air, and living organisms that form the outermost layer of Earth’s surface

Soils uses

providing water, nutrients and anchorage for vegetation, habitat for decomposers, buffer between atmosphere and groundwater, ion exchange properties

3 categories of soil organic matter

decomposing plant and animal matter, resistant organic matter (humus), living organisms such as earthworms, bacteria, or fungi

Mineralization

The decomposition of plant and animal matter that results in the release of nutrients (esp nitrogen, phosphorus, and sulfur)

Gravitational water

water movement down through soil due to gravity

Field capacity

occurs when all smaller pores are filled with water and the larger pores filled with air

Capillary water

water held by surface tension on small particles in the pore space

Hygroscopic water

water that is held in a very thin layer around each individual soil particle

Soil formation

slow process that takes thousands of years

Soil horizons

develop as a result of transfer processes (translocation, transformations, addition and removal) that occur in the open system of soil

Soil Profile

vertical cross-section from the surface down to the bedrock that displays distinct horizontal layers

Finger assessment of soil

Method collecting a sample of soil and moistening it, before feeling it between fingers for different soil proportions

Sieving

involves the use of sieves with different sized meshes to trap stones, sands, clays, and silt

Sedimentation

method where a sample of soil is first placed into a cylinder of water. Cylinder is shaken and then allowed to settle to see proportion of soil

Soil bulk density (SBD)

influenced by 3 main factors: proportion of mineral matter and organic matter, soil texture, and compaction of ground. SBD values increase with soil depth due to compaction and the presence of smaller quantities of organic material

Shelving

the use of sleeves with different sized meshes

Primary minerals

minerals from bedrock that are resistant to weathering, such as mica and feldspar. Mainly present in sand and silt

Secondary minerals

products of chemical weathering and are present in clay.

Podzolization

a form of leaching under acidic conditions in which iron and aluminum are leached from the upper horizons and deposited in the lower horizons

Sodicity

the presence of large amounts of sodium ions in relation to other cations

Incorporation of organic matter

includes plant litter, dead animal biomass and manure, produces a surface horizon that is rich in organic matter. Dead organic matter is largely found on uppermost layer of the soil having got there by litter-fall

Podzol

Shows the 3 distinct layers representing the different stages of decomposition

Fresh Litter layer (L)

at the surface contains recognizable plant remains

Fermentation layer (F)

where decay is active, and the plant remains are difficult to recognize

Humus layer (H)

where all plant material has been degraded

Humus

the black substance with a loose, crumbly texture formed by partial decay of dead plant material. Contributes to soil texture by improving mineral nutrient retention, water retention and aeration

Weathering

the breakdown of rocks in situ (without movement). Also influences soil texture (size of individuals soil particles)

2 types of weathering

mechanical (physical), which is the development of smaller particles of the same rock. Chemical weathering is the transformation of granite into kaolinite (china clay)

Podzolization

form of leaching under acidic conditions in which iron and aluminum are leached from the upper horizons and deposited in the lower horizons

Precipitation

may include several solutes such as calcium, nitrates, chlorine, potassium, sulfates, bicarbonates, of sodium and magnesium, and dissolved gases (important for the transfer of nutrients

Anthropogenic inputs

composting, fertilizers

Composting

can improve the physical, chemical and biological characteristics of soil, soil organic matter and nutrient status. Has an equalizing effect on the annual.

Composting effects

equalizing effects on seasonal variations of water,soil, and air heat balance and availability of plant nutrients, off-set decline in soil fertility and improve plant germination conditions from better aeration and moisture retention, lowers SBD due to addition of low-density organic matter in the soil means more pore space, contains lots of valuable plant nutrients including nitrogen, phosphorus, etc.

Fertilizers

human-made products that are used to increase the level of nutrients in the soil and enhance plant growth.

Agro-chemicals (pesticides, herbicides, and insecticides)

organic compounds such as pesticides, oil, tar, chlorinated hydrocarbons and dioxins are widely used in agriculture.

Impact of pesticides

older pesticides can affect ‘non-target’ species, affect soil adsorption onto clays and organic matter, Some pesticides such as DDT can build up in soils and in the tissue of living organisms, becoming toxic, large-scale use reduces biodiversity in soil, as microorganisms are killed

Irrigation

additional input of water into agricultural systems to encourage plant growth.

Sodicity

presence of large amounts of sodium ions in relation to other cations. (weakens bonds between soil particles)

Natural inputs

can originate from within the ecosystem e.g. from the weathering of bedrock and litter from vegetation and decomposition

Decomposition

process whereby complex organic materials in dead plants and animal tissues are broken down into their original inorganic materials such as CO2, water, minerals, and elements

Organic decomposition

involves 3 processes: rapid leaching of soluble chemical products, mechanical breakdown of dead organic matter through wetting and drying cycles, freezing, and thawing, biological degradation involving the feeding on dissolved organic matter by animals and oxidation.

Erosion

Water erosion

water causes soil erosion through raindrop impact, overland flow and flow in channels. Water can also cause landslides on steep slopes

Wind erosion

occurs on dry, bare soil, the main factors that influence wind erosion are wind speed and particle size.

Water and mineral absorption by roots

water is removed from soil by plants, and transferred up the plant through the xylem and eventually lost from plants to the atmosphere by evaporation

Leaching

Rainwater is naturally acidic, as it moves down through the soil, it reacts with and removes basic cations from the soil solution and those adsorbed to the clay and humus particles.

Diffusion of gas

diffusion of gas occurs when there is a greater concentration of molecules or ions at one point compared to another

Evaporation

the diffusion of water from exposed water surface such as those in lakes, rivers, soils, and plant surfaces. The rate of evaporation is greatly affected by solar radiation, which provides the energy needed to convert liquid water into water vapour.

Evaporation of water and heat loss

heat loss occurs in the form of out-going long-wave radiation. Heat loss is greatest at night in those areas where there is limited cloud cover and/or vegetation cover

Infiltration

the process by which water soaks into or is absorbed by the soil. Distinguished from percolation through the zone of aeration toward the water table

Infiltration capacity

maximum rate at which rain can be absorbed by soil in any given condition

Percolation

water moves slowly downward from the soil into bedrock.

Groundwater

occurs in the sub-surface/underground in the pores of soils and rock.

Water table

The upper layer of the permanently saturated zone (where nearly all pore spaces are filled with water

Aeration zone

the zone that is seasonally wetted and seasonally dries out

Aquiclude/aquifuge

impermeable rocks that prevent large-scale storage and transmission of water

Reasons why groundwater recharge occurs

infiltration part of total precipitation, seepage through the banks and beds of surface water bodies, groundwater leakage and inflow from adjacent aquifers and aquicludes, artificial recharge from irrigation

Biological mixing

can mix the layer of a soil

Aeration

compared to the atmosphere above the soil, soil air has a lower concentration of O2 but a higher concentration of CO2

Erosion and leaching 0 erosion can remove material from one soil and transport it to a soil in another area.

Transformations

can change the components of the whole soil system

Types of soil transformations

decomposition, weathering, nutrient cycling, and soil salinization

Decomposition (transformation)

organic matter that has been added to the soil is transformed into humus and mineral elements. Returns nutrients that were taken by plants

Weathering

central to soil development and provides soil with many of its nutrients. Also breaks down rock and enables erosion and transport

Nutrient cycling

Nutrients are taken in by plants and built into new organic matter either in gases or soluble salts.

Soil Salinization

Capillary forces bring water to the surface where it may evaporate, leaving behind any soluble salts that it’s carrying

Soils provide a medium for plant growth

Provide anchorage for roots, supply of water, and air, and key nutrients.

Physical soil characteristics that may restrict root growth

Mechanical impedance may prevent roots from growing, absence of cracks, shortage of O2

Chemical soil characteristics that may restrict root growth

high aluminum concentration, low nutrient supply, phytotoxic chemicals, anaerobic soil

5 groups of microorganisms

bacteria (mostly heterotrophic), Actinomycetes, Fungi (heterotrophic), Algae, Protozoa

Soils role in recycling

Store and regulate nutrients in the nutrient cycle like leaves, which are broken down for use in plants. Decomposition also breaks down organic material allow other organisms to utilize its nutrients

The carbon cycle and soil

most of the carbon is stored in soil rather than atmosphere, and during photosynthesis, plants convert atmospheric CO2 into plant matter, and after earth the plants decay on soil. Soil organisms consume the left over matter and release the water, heat and CO2 back into the atmosphere

Sandy soil

low primary productivity due to poor water-holding capacity and low nutrient status

Clay soil

quite low primary productivity due to poor aeration and poor water infiltration

Loam soil

high primary productivity due to medium infiltration rate, water-holding capacity, nutrient status, and aeration

Light soil (Workability of soil)

coarse-textured and are easily drained of water and nutrients, but warm up quickest and allow early growth

Heavy soil (Workability of soil)

contains more than 25% clay and are fine-textured, water- and nutrient-retentive