While discussing the soil salinization, salts in lower amounts are usually harmless but due to human activities salts level has been rise up that can affect soil quality, plant metabolism, and microbial activities. Conventional methods are not enough to treat the soil salinity.
Human activities like improper tillage, poor quality irrigation, use of fertilizers or pesticides and lack of crop scheming. In this case, salt-tolerant plants like halophytes are weighed up for their ability to remediate the salinized soil and fend off leaching of salts in surface and groundwater.
Most of the plants are sensitive to salinity but halophytes have developed a mechanism to bear high salinized conditions. Some plants remove through their roots, some sequesters them in their central vacuole and few others exclude salts through salts gland which are present on the leaf surface. The extraction of salts by plants by secretion and sequestration are reviewed and implementation strategies are economically feasible with no side effect.
Salt affected soils
Worldwide 1125 million hectares affect with salinity in which 76 million (ha) are affected by human activities. In Pakistan salt-affected area is 6.30 million (ha), saline soils are present over 1.89 million (ha) of total salt-affected soils. Saline-Sodic soils affects 1.85 million (ha) of area in Pakistan. Sodic soil presents 0.028 million (ha) area of Pakistan.
Salt affected soils are the soil that is affected with salt that can b soluble in water or may not. It can affect plant growth and the metabolism of plants. Soil salinity also affects the structure of soil that can inhibit plant growth. The salts that are present in the soil are present in exchangeable sites of soil. Salinity can be decreased by physical, chemical and engineering approaches. Saline soils are also called “white alkali“.
The soil in which sodium salts area present in excess amount are called “Black Alkali”. Saline soils pH is between 7.55 to 8.5 and EC greater than 4. SAR of saline soil is less than 13. Sodic soil pH range is more than 8. EC of sodic soil is less than 4. SAR of sodic soil is greater than 13. In sodic soil, soil permeability has decreased and plants root cannot penetrate. Saline-Sodic soils have both characteristics of saline and sodic saline. Salts present in soil are Cl-, Ca+2, Na+2, Sulphates, and Magnesium.
| Soil classificaton | EC | pH | SAR |
| Normal Soil | <4 | <8.5 | <13 |
| Saline Soil | >4 | <8.5 | <13 |
| Sodic Soil | <4 | 8.5 – 10 | >13 |
| Saline-Sodic Soil | >4 | <8.5 | >13 |
Anthropogenic Activities
Tillage Practices
Tillage practices use to prepare a field for an annual or seasonal crop. In sodic soil deep tillage required to remove hard pane. Overuse of the same type of tillage instruments can make hard pane in soil that can give a tough time for both leaching and root penetration. To escape that case use minimum or no-tillage practices. In some case salt leach down in lower surface of the soil but due to tillage practices it mixes in normal soil. When precipitation high it can convert into a soluble form and may damage to normal soil. So, by this type of tillage practices can cause salinity in soil. When we mix normal soil to salts affected soils and then irrigate it with water. Salts avail in soluble form and also disturb normal soil.
Use of fertilizers
In saline soil we are totally conscious about fertilizers use. Due to pH difference we cannot use fertilizer in normal routine time or amount. In sodic soil we cannot use DAP (Diammonium Phosphate) due to high pH of soil. In sodic soil we can use SSP (Single Super Phosphate), and TSP (Triple Super Phosphate).In saline soil we can use CAN (Calcium Ammonium Nitrate), and NP
Poor Quality Irrigation Water
In Pakistan’s soil salts are already present and underground water also salty. When farmers applied this type of poor-quality water it increases salinity level in the soil. Due to hard pane or waterlogging problem salts cannot be leached down and present in the root zone. Salts present in solid form are less harmful than soluble form. When salty water applied salts present in the soil also convert to a soluble form that plants can uptake easily.
Use of municipal sewage water
To gain maximum yield farmer use every adversely affected material that effect salt level in soil. Sewage water use to gain maximum yield manufacturing. But in sewage water detergents, salts, phosphates and water softener agents. When a farmer applied such kind of water to gain superlative production it increases salinity in soil due to the presence of salt and chlorides. Sewage water may also contain many pathogens such as Bacteria, Viruses, Protozoa, and parasites. The use of such kind of water may also cause disease in humans and animals because of the presence of parasites. For agriculture purposes, sewage water must treat or may dilute in good quality of water to decrease the effect of chemicals.
Industrial waste water
When industrial water adds into rivers or canals without any treatment it may cause effect soil salinity level. Due to seepage and other factors it reaches agriculture land through irrigation water and rain-fall runoff. In industrial water, it may contain salts or chemicals that can affect soil salinity and structure of the soil, due to the access amount of Na+2 permeability of soil disturbs. Waste water of industrial state treated and then put it into canals and rivers or may use for agriculture and other industrial use.
Man-made sodium sources
Another source of human beings, besides agricultural fields or groundmass, is sodium salts, as well as wet coaling towers using sea-water to eliminate heat generated in various industries located near the coastal area of the sea. In Coal power plants, the burning of coal and lignite produces some ash that can produce CaO. It is easily dissolving in water and easily moves into canals, Rivers, and Seas. This water relevant to irrigation water and causes salinity in the soil.
Phytoremediation of salt-affected soil
Phytoremediation is an operation in which plants are used to treat soil that is influenced by salt. No physical, Chemical and Biological approaches needed to reclaim that type of soil. These approaches are not durable and long-lasting. But phytoremediation can be a permanent solution to this kind of soil.
In phytoremediation, we grow such types of plant species and types that can grow on salt-affected soil and also grow with salty water. Phytoremediation is not only used for the improvement of salt-affected soil but also use to clean the environment. It can provide us good quality of food, fodder, and fuel wood and raw material and can increase the economy of our producers. Phytoremediation is used only in saline soil and not proper in sodic soil due to low permeability.
In worldwide phytoremediation use at broad scale to utilize the saline soil or saline-sodic soil. We can use Phytoremediation in Pakistan because our soils are mostly saline or saline-sodic. The amendments that we adopted in few years ago were also beneficial but phytoremediation is better than all others. The plants and crops that we use as phytoremediation are: barely, guar, chickpea, canola, oats, soybean, sugar Beet, sugar cane, sunflower, wheat, peanut, rice, etc.
The woody plants that can give us both economic and nutritious value are also used as phytoremediation. We can use these plants according to their optimum environmental condition. Such as apple, almond, avocado, Cherry can be grown in cool and maximum precipitation area. In Barani area fruity plants and some seed plants can grow such as mango, orange, grapes, lemon, grapefruit, and date palm.
Conclusion
Soil salinity adversely affect the agriculture production. If Sodium salts present in soil it distorts soil structure and reduces the permeability of the soil. Soluble salts affect the metabolism of the plants and can cause drought conditions. If we want salt free soil, we must reduce all these anthropogenic activities to resolve the effect of salts. If we want to use these anthropogenic activities, we must have information about its beneficial and adverse effect. After information about these amendments, we can resolve the salinity level of our soils. Proper check and balance of irrigation water, sampling of soil, and amendments to resolve these issues.
Uses of salt-tolerant crops are beneficially for the reclamation of salt-affected soils. Seedling rate should be increase to enhance germination rate. Through phytoremediation, we can get biologically and economically benefits. Through reclamation by physical, chemical and biological approaches we can improve soil structure. If we improve the structure of soil agriculture production and yield may enhance.