Soils Flashcards
3 main important functions of soils
key ecosystem services, key biogeochemical services, human uses
what two human factors are driving soil change
economic and population growth
describe the initial stage of soil formation
bedrock is physically fragmented, minerals chemically decompose, minerals reconstituted to clays
where do organic soils form
water-saturated environments
what process leads to the breakdown of rock to form soils
mechanical weathering
what are histosols, characteristics
organic soils, 40cm or more organic material in top 100cm. vulnerable to land use change
how are histosols formed
nutrient runoff from the surrounding landscape leads to growth of aquatic veg. Organic debris fill water body and soil layers eventually form depending on the veg
5 soil forming factors
time, parent materi. climate, topography, organisms
what is the potential 6th factor for forming soils
human intervention
how does climate impact soil formation
rates of physical and chemical weathering, leaching, deposition and precipitation of minerals
how does parent mater. influence soil formation
residual soils develop in situ from bedrock but soil can be from transported mater. too. Specific physicochemical aspects of parent mater.
how does topography impact soil formation
energy exchange and hydrological characteristics. Flatter usually = deeper
how does organic matter impact soil formation
plants needed for accum. of organic matter, symbiotic relationships between lichens and fungi (primary colonisers) facilitate soil devel.
how does biotic aspect influence soil formation
support of soil-based macroorganisms and microorganisms, mineralisation of organic matter to form humus
name several ways that humans have disrupted soil
land use change, drainage pattern disruption, mechanical cultivation of topsoil breaks up peds, cropping patterns, application of irrigation, fertilisers and pesticides, salinisation, pollution
3 stages of soil profile development
weathering of parent material, formation of soil particles and accumulation of organic matter, movement of mater. to different horizons
O horizon
top horizon, organic matter
A horizon
topsoil, lots of bio. activity, darker colour, most fertile usually,
zone of eluviation
in podzols where the clay particles and nutrients are washed out of the A horizon
B horizon
subsoil, thicker, high con. of clay, less water
zone of illuviation
area of B zone in podzols where the clay particles are washed in
C horizon
some parent mater. , transitional, partially weathered
what phase forms the structural skeleton of mineral soils
solid phase= over 50% volume
3 sizes of soil pores
micropores, mesopores, macropores
5 types of soil particles in size order
stones/gravel coarse sand fine sand silt clay
what is soil texture
the size range of particles in the soil
qualitative= the feel
quantitative= distribution of particle sizes ad mass of various size ranges
how are soil types classified
proportion of sand, silt and clay
what is the specific surface area of soil
total surface area of a soil per unit of mass-> can determine type and property of a material
what is the cation exchange capacity
influences the retention and release of nutrients and salts within the soil solution
high clay/organic matter= higher cation exchange capacity
soil fertility
ability of soils to supply nutrients needed for plant growth
how many elements are essential to plant growth
17
how can changing water dynamics change soil processes and composition
swelling or shrinking, porosity, density, pore-size distribution
which pore types allow the use of water by plants
macropores (rapid movement) and mesopores-> hold water against force of gravity which is key for plants
cycle of carbon through soils
plants via photosynthesis, leaf litter, through roots, release of gas and dissolved carbon through respiration
what percen. of terrestrial carbon stores is in soils
80%
key cause of soil organic carbon loss?
land use and change
aim of the 4 pour 1000 initiative
increase soil carbon storage by 4 parts per 1000, use soil carbon sequestration as a negative emission strategy
4 key ecosystem services provided by soils
food security, water quality and provision, climate regulation, biodiversity
what does SOC stand for
soil organic carbon
5 ways rocks are eroded chemically to form soils
hydrolysis, carbonation, hydration, dissolution, oxidation and reduction
how does hydrolysis occur
most common form of chemical weathering: water dissociates into hydrogen and a hydroxyl ion which attack the bonds holding minerals together
what kind of change do minerals undergo to become oxidised or reduced
chemical change through an electrostatic charge
