5.1 Introduction to soil systems Flashcards
Define Soil
Soil is what forms the outermost layer of the Earth’s surface, and comprise weathered bedrock (regolith), organic matter (both dead and alive), air and water.
The soil interacts with the atmosphere, lithosphere, biosphere and hydrospher
What are the four main functions of soil
- Medium for plant growth
- soil supplies plants with nutrients, water and a place for them to anchor (roots)
- Water storage and purification system
- Provides a habitat for over 1/4 of all living species (bacteria, insects, mammals)
- these organism modify the soil
- Soil modifies the atmosphere through respiration of soil organisms and plant roots
State meaning in order: pedosphere, litosphere, hydrosphere, atmosphere and biosphere
- pedosphere → SOIL
- litosphere → rocks
- hydrosphere → water
- atmosphere → air
- biosphere → living
Draw a diagram of the interactions between the spheres
En tu docs foto 8
State the 5 factors affecting soil characteristics
- Climate
- Organisms
- Relief
- Parent Material
- TIme
Why is soil a system?
Soil is a system because it has biotic and abiotic factors which interact with one another
State two types of organisms that reside in soil
- micro-organism: bacteria
- macro-organism: earthworms
how do micro and macro organisms contribute to the soil system?
- Leaves and organic debris accumulates on the surface of the soil where it will be broken down by decomposers in the top layer of soil
- The process starts with bacteria and fungi and ends with small insects (mites, springtails and earthworms) that consume the dead organic matter (DOM)
- Earthworms perform the final stage of decomposition. They breakdown the DOM and convert it to humus then as they move to the lower horizons they mix it into the soil (biological mixing)
- They (earthworms) distribute microbes throughout the soil in their castings; they increase the availability of phosphorous, they aerate the soil and improve drainage and they mix the soil.
Inputs of the soil system (4)
Minerals,organic matter,airandwater.
- Minerals
- come from weathering of parent material
- Organic matter
- comes from the living organisms in the soil
- Gases
- Certain plants fix atmospheric nitrogen and change it into nitrates and ammonia compounds in the soil
- water
stores of the soil system (5)
Organic matter, Organisms, minerals, water, nutrients
- organic matter
- dead organic matter (DOM) that comes from the biotic elements of ecosystems.
- → anything that used to live and decomposes ahi → used for growth
- So the DOM is a store of nutrients that can be taken up by the plants to be used for growth.
- organisms
- →add nutrients to the soil when they deposit waste.
- minerals
- form the body of the soil
- water
- nutrients
Outputs of the soil system (3)
- loose organic matter from top layer (blown off)
- plants take nutrients from soil for growth
- animals eat the soil
Processes transfers and transformations of the soil system
- Leaching and evaporation
- Decomposition
- Weathering
- Nutrient cycling
Leaching and evaporation
- Leaching is the process by which water moves through the soil and carries away dissolved substances from the upper soil layers, transporting them deeper into the soil profile
- Evaporation: high temperatures draws water up to the surface where it evaporates → water evaporates and salt is left begind → salinization of soil
Decomposition
- Decomposers break down the DOM in the soil and release the plant nutrients
→ transformation
Weathering
- The breakdown of parent material through the process of weathering adds minerals to the soil
- physical weathering: breaks the rocks up in to smaller pieces and thus gives plenty of raw material for soil formation
- chemical weathering: dissolves the minerals in rocks and leaves behind very little raw material for soil formation
Nutrient cycling
Organic matter, such as dead plants and animal residues, decomposes into inorganic forms, releasing nutrients like nitrogen and phosphorus into the soil
Draw the soil profile
Dibujo 9 en el docs
Explain and state each horizon of the soil profile
O horizon
A horizon
B horizon
C horizon
O horizon
Top of the soil and includes all the DOM that accumulates on top of the soil
A horizon
- top soil or mineral layer
- usually dark in colour due to the high proportion of organic matter → zone of highest biological activity
B horizon
Sub-soil and tends to be the zone of illuviation or accumulation
C horizon
- Decomposed parent material. In most cases this layer is not really affected by soil processes but it has weathered
- Layer may contain large lumps of parent material.
INTERVENTION: what is hummus?
Dark, organic material that forms as a result of the decomposition of plant and animal matter within the soil
How does soil texture say what type of soil it is (table you have to memorize)
Particle: Sand - coarsest particles - Size (mm) 2.0 - 0.05
Particle: Silt - Size (mm) 0.05 mm - 0.002
Particle: Clay - finest particles - Size (mm) Less than 0.002
Properties of sandy soil
- The large particles create large pores spaces between them
- Well drained so rarely get water logged
- Subject to drought in times of low rainfall
- Warm up quickly in summer due to high air content
Properties of clay soil
- Small particles give small pore spaces
- Poorly drained and prone to water logging
- Take a long time to dry out after rainfall
- Warm up slowly in summer due to high water content
Properties of silt soil
smaller pore spaces so their properties are between sand and clay
What is loam soil
Relatively even mix of sand, silt and clay is called a loam and it is ideal for agriculture
How does soil texture impact primary productivity
Soil texture impacts primary productivity by influencing nutrient availability, water retention, root growth, and soil aeration
- Clay soils retain nutrients but may become waterlogged
- sandy soils drain quickly but require more irrigation
- Silt and sand promote root growth, while clay can hinder it
- Soil erosion is also more likely in sandy soils
