A LEVEL ENVIRONMENTAL SCIENCE: Soils
Terms in this set (34)
soil is a layer of broken down organic and inorganic matter, which acts as a 'bridge' between the inorganic world and life.
components of soil
- minerals (rocks)
- organic matter
- soil pH
- soil temperature
- soil texture
- soil structures
soil layers; O horizon
- litter layer
- hummus layer
soil layers: top soil; A horizon
- A1 layer
- A2 layer
- minerals leached out of this layer by rainfall percolation through. horizon gets lighter towards the bottom.
soil layers: subsoil; B horizon
- leached minerals collect in lower layer of B horizon, often forming a hard pan.
- accumulation of minerals.
soil layers; C horizon
- weathered bedrock.
- refers to how coarse soil particles are. includes proportions (%) of sand, silt, and clay.
- controlled by parent rock (e.g. bedrock) and how easily it is weathered.
soil texture; grain sizes
sand = 2mm
silt = 0.002 - 0.02mm
clay = <0.002mm
- granules in top part of soil a crumbly. give good seedbed.
- rounded-blocky peds in topsoil for good drainage and aeration.
- angular-blocky peds form transition between topsoil and subsoil. good drainage.
- prismatic-blocky peds of subsoil provide good drainage.
poorly structured soil
- platy structures form surface cap due to bad cultivation techniques and poor structure.
- large peds in topsoil limit drainage and aeration.
- platy structures develop under topsoil due to use of heavy machinery. inhibits drainage and aeration.
- columnar peds merge in subsoil. poor drainage.
impact of soil texture on fertility
size of soil particles will impact the ability of things to grow in it by influencing other factors such as:
- infiltration of water through the soil
- amount of air that can enter
- pore spaces
- describes how soil components fit together into peds.
- clay particles in soil clump together via cohesion and form a ped.
types of peds (smallest -> largest)
- sub angular blocky
factors that deteriorate or destroy soil
- removal of vegetation
- excessive moving and handling of soil.
effect of platy soils on fertility
- platy soil means that roots cannot penetrate the ground and, therefore, cannot grow and add organic matter.
- platy soil means less drainage and, therefore, water-logged soils.
effect of crumb soils on fertility
- may not hold enough moisture from plant growth.
improvement of soil structure
can be achieved by aerating the soil, e.g. by small burrowing organisms such as worms or maggots, or by ploughing.
- moisture is essential as it supplies nutrients and water to plants.
- plants can only take up water that enters the soil during precipitation and infiltrates the pore spaces.
- soil is heated by incoming solar radiation.
- vegetation insulates the ground and reduces the range of temperature extremes.
- wet soils heat and cool more slowly than drier soils.
effects of warmer soil
- increases enzyme activity
- encourages root growth
- encourages seed germination
- increases decomposition and nutrients.
pH of soil has major effects on the availability of nutrients in the soil.
soil erosion; wind
- when soils with little clay content dry out, they become loos and there is little cohesion between the particles.
- if the soil is unprotected, it will be blown away by the wind. this means some areas will loose their soil and other will be covered in dust.
soil erosion: rain splash (water)
- soil particles are dislodged by splash of raindrops and dispersed in all directions; downhill may travel further.
- overtime, can cause downward movement of soil.
soil erosion: surface runoff (water)
- caused by surface runoff when the infiltration capacity of the soil has been exceeded.
- occurs when rainfall is heavy or prolonged, or if the soil is relatively impermeable so more of the water flows over the ground surfaces.
1930 dust bowl, usa
- main states = Colorado, Kansas, Oklahoma, New Mexico, Texas.
- poor agricultural practices and years of drought caused the dust bowl.
- by the end of the decade, nearly 75% of the topsoil had been blown away in some areas.
managing soil erosion; mulch
- a protective covering.
- can be straw, compost, wood chip, saw dust.
- protects soil where vegetation has not yet grown.
managing soil erosion; wind breaks
- can be trees, shrubs, fences, concrete walls, etc.
- deflect wind stream and reduce wind velocities. wind does not impact soil as severely, so becomes ideal for crops to grow.
managing soil erosion; contour ploughing
- creates gullies that increase velocity of runoff and cause more rapid erosion.
- water flow is stopped by ploughed furrows and loses its kinetic energy, so it can no longer carry soil particles.
- soil particles are deposited in the furrow.
managing soil erosion; terracing
- sloping land is cultivated by creating a series of narrow fields held in place by retaining walls built along the contours.
- water flowing over the walls flows quickly but slows over the fields, so it infiltrates into the fields.
- runoff water moves rapidly over the soil surface, cutting well defined finger shaped grooves that appear as thin channels or streams.
- rill erosion is the removal of soil by concentrated water running through small streams.
- deep channel that is enhanced by surface runoff.
- water movement is faster, creating a deeper channel.
- soil particles that are displace tend to be larger than in rill erosion due faster paced water.
human activities that increase soil erosion rate
- vegetation removal
- ploughing vulnerable soil
- reduced soil biota
- soil compaction
methods of reducing soil erosion
- long term crops
- zero-tillage cultivation
- tied ridging
- rows stones
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