Sources of Salt-Affected Soils

Soluble salts such as MgSO4, MgCl2, CaSO4, or CaCO3 may be present in large quantities in some soils especially in arid and semi-arid regions. These soils are called salt-affected (halomorphic) soils whose salt content is high enough to cause negative effect on plant growth.

These halomorphic soils are either saline, alkaline or even saline-alkaline depending on the percent of total soluble salts that is sodium content.

Sources of Salt-Affected Soils

The salt-affected soils occur mainly in arid and semi-arid regions. Under these agro-climatic conditions there is usually accumulation of salts in the upper layers of the soils such as NaCl, Na2 SO4, MgSO4, MgCl2, CaSO4, or CaCO3.

Two major conditions could give rise to excess salts in the plough soil layer, namely:

  • Evapo-Transpiration: In the dry regions, evapotranspiration might be in excess of precipitation especially during the dry period of the year. This leads to whitish surface as a result of residue of inorganic salt left behind after escape of water vapour.
  • Rise in Ground Water: Underground water contains salts. When the water rises, it brings up salts and when it goes down again it leaves the salt on the soil surface.

Other conditions that give rise to salty soils are poor drainage and seepage from other areas, soluble salts from the weathering of primary minerals, coastal soils with oceanogenic salinity and desert salinity usually caused by wind-borne salts.

Read Also: Physical Properties of Soils (Soil Physical Properties)

Saline Soils

The ability of ions in water to conduct electrical current gives rise to the use of electric conductivity in quantifying total amount of soluble salts in a soil sample.

A soil is described as saline if it has electrical conductivity (of saturation extract) greater that 5 MS Cm-2 (4 million hos/cm) or 4 decisiemens per meter (4ds/m) or has a low sodium absorption ratio (SAR) at 250C, a soluble sodim content of less than half the total soluble cations and a pH value usually between 6.3 – 8.5.

The predominant saline soils have neutral to alkaline reaction but acid saline soils also occur. Acid saline soils exist in coastal or marine flood- plains as acid sulphate soils. In these coastal areas, water logged, sulphur-rich soils become extremely acidic after a dry period due to oxidation of sulphur to sulphate.

 The pH value could drop from about 6.7 to less than 2.0 during oxidation. When such soils are submerged, the presence of hydrogen sulphide becomes toxic to plants, preventing the cultivation of crops such as rice. When such soils are dried and therefore oxidized, characteristic yellow streaks of sulphates of iron and aluminum are produced and may form a crust on the soil surface.

Saline soils are agriculturally unproductive because they give poor growth of plants and poor crop yields. In saline soils osmotic pressure of soil solutions is usually too high for plants to absorb sufficient nutrients and water.

The concentration of salts outside the roots is usually too high that water may be withdrawn from the plant roots causing plasmolysis or oxosmosis and poor root growth or even outright death of roots.

Other deleterious effects of soil salinity on plant growth are reduced root elongation rate, reduced root permeability due to upset in plant hormonal balance and reduced transpiration rates.

Increase soil salinity results in ionic imbalance of the soil solution, and in turn, affect the nutritional balance of the plant. The high pH of saline soils affects solubility of many nutrients, soil structure, soil strength, aeration, hydraulic and ionic conductivities.

Read Also: Factors Affecting Availability and Fixation of Potassium Soils

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Benadine Nonye

An Agric. Consultant & a Writer (With over 12 years of professional experience in the agricultural industry) - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education... Visit My Websites On: - It's All About Agriculture, The Way Forward! - The Most Reliable Global Agricultural & Waste Management Forum! - The Most Reliable Agricultural Job Board! - Your Reliable E-Learning Agricultural Academy! - For Proper Waste Management and Recycling Practices. Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4ProfitsTV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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