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 Sourcespetroleum 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;

polychlorinated biphenyls (PCBs), transformers, circuit breakers, electromagnets

organotin compounds PVCs with tin compounds / antifouling compounds (coatings or paints) / fungicides / pesticides / biocidal agents;

semi-volatile organic compounds (SVOCs)

diesel and motor oils