Tree Planting in Problem Soils - Salt affected Soils

Salt affected Soils


These soils are those in which either the salt contents of lower horizons concentrate in or on the soil surface or normal proportion of various cations and anions present in soil is disturbed in a big way by excess or shortage of certain ions. This redistribution of salts of salts in soil profile is generally caused by the rising of water table accompanied by intensive evaporation from the surface. The saline water moves up through capillaries and evaporates into the atmosphere while leaving the salts on the soil surface. These salts are frequently seen in the form of thin white crust in the saline area. This crust is quite conspicuous during winter. It has been estimated that about 1/4 to 1/3 of our irrigated area has gone out of production because of salinity. Product vising these areas by tree planting is a major breakthrough.
These soils are those in which either the salt contents of lower horizons concentrate in or on the soil surface or normal proportion of various cations and anions present in soil is disturbed in a big way by excess or shortage of certain ions.

Salinity of soils is rightly considered as enemy number one of World’s Agriculture. In Pakistan about 16.75 million acres area (33% of cultivated land) are already salt affected to varying degrees. It has been estimated that about 200 acres of our fertile irrigated crop land goes out of production per day because of salinity. The plants growing in saline or sodic soils have to face some or all of the following problems:

Ø  Concentration of soil solution is greater than that of cell sap in the root, which results in loss of water from the root.
Ø  The imbalance of ions in the soil solution may have toxic effect on cell physiology.
Ø  Water drainage, root penetration and root respiration are restricted due to deflocculation and rising water table.
The solution of above mentioned problems is based on lowering of water table and ensuring free drainage. This would stop the upward movement of salts. The excess salts on the soil surface are then simply washed down into deeper layers and into the drains by repeated heavy irrigations. The ionic imbalance and deflocculation is corrected by liberal addition of Ca in the form of powdered gypsum and organic manuring. This treatment cannot be extended to all the affected areas. It is thus logical to turn to biological approach which is sample, cheap and self-perpetuating. The following points explain the working of biological approach:
These soils are those in which either the salt contents of lower horizons concentrate in or on the soil surface or normal proportion of various cations and anions present in soil is disturbed in a big way by excess or shortage of certain ions.

Ø  Woody vegetation lowers the water table effectively; trees being natural tube wells.
Ø  Saline water moves up through vegetation rather than moving through soil capillaries and leaving salts on soil surface. In the presence of vegetation, water transpires into the atmosphere while leaving the salts in the plant tissue.
Ø  Vegetation canopy and litter drastically reduce evaporation from soil surface.
Ø  The addition of organic matter, root penetration and activities of associated fauna improve the soil structure and ensures good drainage. This facilitates the washing down of excessive salts from the soil surface into deeper horizons. It should be noted that these salts are highly soluble in water. A few light irrigations or showers are enough for downward leaching salts.
Ø  Periodic removal of vegetation reduces the total salts concentration in the site.
These soils are those in which either the salt contents of lower horizons concentrate in or on the soil surface or normal proportion of various cations and anions present in soil is disturbed in a big way by excess or shortage of certain ions.

There a number of woody species which can tolerate varying degrees of salinity are called Halophytes. It may be pointed out that different halophytic species use various adaptations to overcome the problem of salinity. It is generally considered that halophytes have to overcome the additional problem of physiological drought. It has been reported that many drought tolerant plants can easily overcome salinity provided there is no hindrance to their root respiration. Fortunately it is quite easy to select suitable salt tolerant species from our indigenous flora i.e. Acacia, Tamarix, Azadirachta. Some exotic species have also been very useful for this purpose i.e. Eucalyptus and Atriplex.
These soils are those in which either the salt contents of lower horizons concentrate in or on the soil surface or normal proportion of various cations and anions present in soil is disturbed in a big way by excess or shortage of certain ions.

Following techniques should be kept in view while planting:
Ø  Use large and vigorous plants. Entire plants with a ball of earth or potted plants be selected. Shoot or root cutting etc. must be avoided.
Ø  For pit planting, top 8 cm or more of saline surface soil be removed from planting site and should not be used for re-filling the pit. Relatively large pit be dug, i.e. 1 meter diameter and 1.25 meter depth. If possible powdered gypsum farmyard manure and/or coarse sand be mixed with dug-out soil and this mixture be used for filling the pit; the surface of filled pit should be 15 cm below the soil surface to retain added water. It is better to cover the pit surface with 5-8 cm thick layer of coarse sand of litter. This layer would cut off evaporation and prevent salt accumulation on pit surface. A ridge should be provided around every pit to prevent surface run-off of saline water from bringing salts from surrounding area into the pit.
Ø  Fresh water should provide at short regular intervals during the initial stages. Later on the watering intervals may increase along with an increase in its intensity.
Ø  Plants should be rigorously protected from climatic and biotic stresses such as frost, hot dry winds, extremes solar radiation, extremely high temperature of soil surface, trampling and browsing, etc. Most plants can overcome one problem, waterlogging, drought etc. at a time; plants, however, fail to survive when these are faced with two or more problems simultaneously. One should, therefore, try to minimize the number and intensity of problems. Fluctuations of surface soil temperature should, for example, be moderated by providing litter mulch and keeping the soil moist.
Ø  If there is very heavy deposition of salts, it is better not to undertake any planting on large scale unless it is supported by research and experience.
Ø  If salinity and alkalinity are found coupled with high water table, deep drains will have to be provided much before planting as a vital part of site preparation.


These soils are those in which either the salt contents of lower horizons concentrate in or on the soil surface or normal proportion of various cations and anions present in soil is disturbed in a big way by excess or shortage of certain ions.

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