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What is salinity and what are the main causes? Salinity is the word used to describe the salt content of soil or water. When this salt content is excessive it degrades water quality and land productivity. Soluble salts are often found in water and soil but usually not in sufficient concentrations to affect plant and animal survival. When the salt in the soil or water becomes excessive then plants start to die off and the water becomes uninhabitable for marine plants and animals, also the soil that is affected will not be able to produce any crops for farmers after a period of time. Dry land salinity is caused when the rising of the water-table brings natural salts in the soil to the surface. The salt remains in the soil and becomes progressively concentrated as the water evaporates or is soaked up by plants. One of the main causes for rising water-tables is the removal of deep rooted plants, perennial trees, shrubs and grasses and their replacement by annual crops and pastures that do not use as much water. The diagram above explains how the dry-land salinity occurs when the water table rises. How salinity can be identified in the landscape These will vary with plant species, but include patchy growth in pastures, or slow growth, stunting and reduced yield in crops. As salinity levels increase, stunting becomes more noticeable in crops and leaves become dull or take on a blue-green colour and become coated with a waxy deposit. Initial impact on grapevines is a reduction in shoot growth and yield due to toxic levels of chloride and sodium, while in vegetable crops yellowing of younger leaves precedes yellowing and death of margins and tips in older leaves. Orchard plants will suffer reduced yields. Increasing salinity levels and subsequent chloride and sodium toxicity cause yellowing of grapevine leaf margins, progressing inwards until leaves drop off, while increasing levels of borates will initiate black spots on the leaf margin and a cupping effect on leaves.
Approximate Word count = 1212
Approximate Pages = 4.8
(250 words per page double spaced)
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