effects of salinity on plant growth

7/28/2019 Effects of Salinity on Plant Growth

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EFFECTS OF SALINITY ON PLANT GROWTH

Salinity, affects plant growth in diverse ways and these are a few of them;

1)Plants that are adversely affected by salinity grow more slowly and are therefore stunted

2) Leaves of salt-affected plants are smaller but may be thicker than those of normal plant.

3) Chloride ( but not Sulfate) increases the elongation of the palisade cells, causing increased

succulence

4)Leaves of salt-affected plants are often darker green than those of normal plants, but in some

species (eg, crucifers and some grasses) thicker layers of surface wax cause a bluish green cast

5) Stunting of fruits as well as leaves and stems occurs (4,8)

6) Salt-affected plants may show no distinctive symptoms; and only comparison

7) Salt-affected soils reduce both the ability of crops to take up water and the availability of

micronutrients.

8) They also concentrate ions toxic to plants and may degrade the soil structure.

CAUSES OR SOURCES OF SALINITY

Primary salinization occurs naturally where the soil parent material is rich in soluble salts, or in

the presence of a shallow saline groundwater table. In arid and semiarid regions, where rainfall is

insufficient to leach soluble salts from the soil, or where drainage is restricted, soils with high

concentrations of salts (“salt-affected soils”) may be formed.

Secondary salinization occurs when significant amounts of water are provided by irrigation, with

no adequate provision of drainage for the leaching and removal of salts, resulting in the soils

becoming salty and unproductive.

1) Improper irrigation schemes management, including:

a) insufficient water application;

b) insufficient drainage;



c) Irrigation at low efficiency (where most of the water leaks into the groundwater) and/or

Over-irrigation contribute to a high water table, increasing drainage requirements and causing

Water logging and salinity build-up in many irrigation projects of the world;

d) Irrigation with saline or marginal quality water, which may be caused by intrusion of saline

water into fresh water aquifers in coastal zones due to over pumping.

2. Poor land levelling - small differences in elevation may result in salinization of the lower

parts, as the

water table is closer to the surface and is subject to greater evaporation;

3. Dry season fallow practices in the presence of a shallow water table;

4. Misuse of heavy machinery leading to soil compaction and poor drainage;

5. Excessive leaching during reclamation techniques on land with insufficient drainage;

6. Use of improper cropping patterns and rotations;

7. chemical contamination. e.g. as a result of intensive farming, where large amounts of mineral

fertilizers

have been applied over a long period of time

What is ESP and SAR?

Sodicity is measured by calculating the exchangeable sodium percentage (ESP) and/or the

sodium adsorption ratio (SAR).

ESP is the percentage of soil exchange sites occupied by Na+, and is calculated by dividing the

concentration of Na+ cations by the total cation exchange capacity (CEC; SW 1). Units of

concentration for ESP are milliequivalents per 100 g (meq/100g).

SAR, on the other hand, expresses the proportion of Na+ relative to the proportions of Ca2+ and

Mg2+, where cation concentrations are in milliequivalents per liter (meq/L)

WHAT ARE THE CLASSES OF SALT-AFFECTED SOILS?

1) SALINE SOILS.

Saline soils contain excessive concentrations of soluble carbonate, chloride and sulfate salts that

cause EC levels to exceed 4 mmhos/cm. The primary challenge of saline soils on agricultural

land is their effect on plant/water relations. Additionally, if salinity in the soil solution is great



enough, water may be pulled out of the plant cell to the soil solution, causing root cells to shrink

and collapse. The effect of these processes is „osmotic‟ stress for the plant. Osmotic stress

symptoms are very similar to those of drought stress, and include stunted growth, poor

germination, leaf burn, wilting and possibly death. Salinity can also affect vegetation by causing

specific ion effects.

2) SODIC SOILS

Sodic soils have a relatively low EC, but a high amount of Na+ occupying exchange sites,

often resulting in the soil having a pH at or above 8.5. Instead of flocculating, Na+ causes

soil colloids to disperse, or spread out, if sufficient amounts of flocculating cations (i.e.,

Ca2+ and Mg2+) are not present to counteract the Na+. Dispersed colloids clog soil pores,

effectively reducing the soil‟s ability to transport water and air. The result is soil with low

water permeability and slow infiltration that causes ponding and then crusting when dry.

These conditions tend to inhibit seedling emergence and hinder plant growth. Sodic soils are

also prone to extreme swelling and shrinking during periods of drying and wetting, further

breaking down soil structure. The subsoil of a sodic soil is usually very compact, moist and

sticky, and may be composed of soil columns with rounded caps. Fine-textured soils with

high clay content are more prone to dispersion than coarser textured soils because of their

low leaching potential, slow permeability and high exchange capacity. Other symptoms of

sodic soils include less plant available water, poor tilth and sometimes a black crust on the

surface formed from dispersed organic matter.

3) SALINE-SODIC SOILS

Saline-sodic soils are soils that have chemical characteristics of both saline soils (EC

greater than 4 mmhos/cm and pH less than 8.5) and sodic soils (ESP greater than 15).

Therefore, plant growth in saline-sodic soils is affected by both excess salts and excess

Na+. Physical characteristics of saline-sodic soils are intermediate between saline and

sodic soils; flocculating salts help moderate the dispersing action of Na+ and structure is

not as poor as in sodic soils. The pH of saline-sodic soils is generally less than 8.5;

however, this can increase with the leaching of soluble salts unless concentrations of

Ca2+ and Mg2+ are high in the soil or irrigation water.

effects of salinity on plant growth

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