Download Soil : soil degradation

Soil
: soil degradation
Salinization
 Salinization is the result of irrigating soils i.e. watering them. Water
used for irrigation usually contains dissolved salts, which are left
behind in the soil after the water evaporates.
 In poorly drained soils, the salts left behind are not washed away and
begin to accumulate in the topsoil. Plants cannot grow in soil that is
too salty.
 Another problem caused by irrigation is that over irrigation/water run
off can remove vital nutrients such as Ca2+, K+ , NH4+ and Mg2+ from
the topsoil.
Soil
: soil degradation
Nutrient depletion
Plants remove nutrients and minerals from the soil. If the soil is
not allowed to recover i.e. allowed time for the removed
nutrients to be replaced through natural processes, the soil
becomes depleted in these nutrients and this will effect future
plant growth. Monoculture i.e. growing the same crop time
after time increases nutrient depletion. Allowing soils to remain
fallow (no crops are grown and nutrients can be replaced) for a
while or use crop rotation i.e. grow different crops which absorb
different nutrients are some solutions.
Soil
: soil pollution
Soil pollution
 This is the consequence of the use of chemicals such as
pesticides and fertilizers. These chemicals can disrupt the soil
food web, reduce the soil’s biodiversity and ultimately ruin the
soil. These chemicals also run off the soil into surface waters
and move through the soil, polluting groundwater.
Soil:
Soil organic matter (SOM)
 SOM is generally used to represent the organic constituents in the
soil, including undecayed plant and animal tissues, their partial
decomposition products and the soil biomass.
 SOM includes:
 main-constituent: decayed plant and animal matter which can be:
 high-molecular-mass organic materials such as polysaccharides and
proteins and
 simpler substances such as sugars, amino acids and other small
molecules
 humus: organic material fully broken down by the micro-organisms in
the soil.
Soil
: SOM
 The functions of SOM can be broadly classified into two groups:
 biological: provides nutrients for the plants, in particular
nitrogen, as it provides amines and amino acids;
 physical:
 improves structural stability,
 influences water-retention properties: the OH- and NH2
groups on the SOM molecules allow hydrogen bonding
between these molecules and water molecules in the soil
 alters the soil thermal properties.
Soil
Pollutants
: pollutants
Sources
petroleum hydrocarbons
crude oil – oil spills
agrichemicals
pesticides, fertilizers, growth hormones (ani
volatile organic compounds (VOCs) petrol, paint thinners, dry cleaning solvents
solvents
paints, dry cleaning solvents
polyaromatic hydrocarbons (PAHs)
tar / coal / crude oil spills / incomplete
combustion of wood/vegetation/waste /
industrial/power station emissions;
transformers, circuit breakers,
electromagnets
PVCs with tin compounds / antifouling
compounds (coatings or paints) / fungicides /
pesticides / biocidal agents;
diesel and motor oils
polychlorinated biphenyls (PCBs),
organotin compounds
semi-volatile organic compounds
(SVOCs)