5.3 Soil Degradation and Conservation
Soil ecosystem change through succession. Fertile soil contains a community of organisms that work to maintain functioning nutrient cycles and that are resistant to soil erosion
The relationship between soil ecosystem succession and soil fertility
influence biotic factors range from organism or bacteria to humans
Indirect influence
bacteria fix atmospheric nitrogen converting into a usable form for plant roots
mycorrhizal fungi on tree roots take up soil nutrients and pass them directly to the tree
decomposers break down litter releasing nutrients into the soil
soil organisms help to mix the soil improving its structure
animal burrows help to aerate the soil
animal faeces return nutrient to the soil
interception of precipitation by vegetation
reduction of precipitation via evatranspiration
Soil degradation is more directly the result of the following
erosion by water and wind
physical degradation
chemical degradation
biological degradation
climate and land use change may accelerate the above factors
loss of structure, soil crusting, surface sealing and compaction
caused by compaction through heavy machine or animal
soil crusting and compaction can increase runoff, decrease the infiltration of water into the soil
water erosion
rainfall intensity and run off
soil erodibility
slope gradient and length
vegetation
wind erosion
soil erodibility
soil surface and roughness
climate
unsheltered distance
vegetation cover
loss of nutrients or organic matter
soil acidification'
salinization
evaporation associates with irrigation
coastal cones: capillary action bring salt to the upper part of soils
soil toxicity
loss of organic matter and biodiversity'
organic matter enters soil mainly
from plants remains and organic manure
loss or organic matter reduce the ability of soil aggregate, result the formation of soil crust
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Human activities can reduce soil fertility
deforestation
intensive grazing
urbanization
certain agricultural practices
removal of some or all of a cover of trees
the greater the proportion of tree removed the less interception occurs
rate of erosion are highest in semi arid areas where there is discontinuous of vegetation cover and seasonal rainfall
Case study: Amazon Rainforest-NW Brazil
The grazing of natural pastures at stacking intensities above the livestock carrying capacity
greater the intensity of grazing, the more vegetation covers is removed
large herds may destroy vegetation cover by trampling
grazers may impact the soil
increases soil compaction, less infiltration
increases potential for soil erosion
Case study: Sahel in Africa
more people now live in cities than in rural areas
requires the removal of vegetation for construction and heavy machinery
increase water flow on the surface of soil
increased run off may lead to extra erosion down stream
irrigation: increase amount of salt in soil
evaporation
paddy field: as water evaporate, salinity increases
coastal and estuaries: salt water intrusion
Case study: Dust Bowl
Soil conditioners
function: corrects the soil's deficiencies in the structure and nutrients
lime
used to reduce soil acidity (increase pH level)
provide important plant nutrient
reduce solubility and toxicity of certain element such as Aluminium
promote availability of major plant nutrients : zinc, copper, phosphorus
increases bacterial activity thus improve soil structure
Cultivation techniques: to reduce water flow
bunding
contour ploughing
terracing
strip cultivation
on the steep slope with heavy rainfall
insufficient contour ploughing
slopes broken up into a series of flat steps terrace with bunds at the edge
a structural measure with an embankment of soil or stones along the contour and stabilized with vegetative measures
the height of the bunds depends on the availability of stones
the ridges formed at the right angles to the slope
to prevent or slow the downward accretion of soil and water
the growing of a cultivated crop in strips
follow an approximate contour of the land and minimize erosion
wind reduction techniques (wind breaks, shelterbelts)
reduce wind speed and rate of evaporation
provide roots at the boundaries of the field, supplying valuable organic matter
provide a habitat for animal, adding general fertility of the field and parcels of the land they surround
cropping and soil husbandry methods
maintaining crops cover as long as possible
keeping stubble and root of the crop after harvesting
planting a grass crop
maintain the action of roots binding the soil
minimize the action of wind & rain on the soil surface
increase organic content allows the soil to hold more water
methods of soil conservation
revegetation
measure to stop bank erosion
measure to stop gulley enlargement
crop management'
slop run off control