Effects of Salt-Affected Soils on Plants Growth
General symptoms of salinity in plants are retarded growth and smaller Plants fewer and smaller leaves. Stunted leaves are generally darker green than normal some plants leaf succulence increases. The other common effects are:
Increase in salinity results in reduction of the amount of water available to the waté This results in increase in osmotic effect, i. e., additional energy is required to absorb from saline soil. However, some plants (halophytes) can adapt to saline environments uptake of salts or by internal production of organic acids.
Specific Ion Effect
Salinity causes specific ion effect, i. e, uptake of a specific ion at the expense of ions. This results in accumulation of toxic amounts of sodium, chloride and boron plants.
Salt Tolerance of Crops
salinity effects salt tolerance of crops, i. e., ability of the crops to survive and produce economic yield on saline soils] This criterion is used. by plant breeders to measure cro ield in terms of relative yield of a species on saline versus non-saline soils over time and space.
Reclamation of Salt-Affected Soils
The process of bringing salt-affected soils back to their normal condition suitable for the growth of plants is termed reclamation.
Methods of Reclamation
The most common practices applied to reclaim the salt-affected soils are:
Leaching is. application of excess water to the soil surface so at the salts may move out of the root zone. Since salts move in with water, it is the main agent causing the accumulation of soluble salts. It is also the main agent for leaching soluble salts and sodium L-OQQ-CU replaced from the soil.
Growing suitable Crops during Reclamation
Suitable crops may be grown on problem soils during reclamation. The activity of growing roots improves soil permeability promoting leaching of salts. Also the carbon dioxide released during respiration increase the solubility of calcium carbonate and facilitate removal of exchangeable sodium. Crops selected must be adaptable to wet conditions and moderately tolerant to salts. Relatively salt-tolerant crops include ka/lar grass, hay, sarson,
alfalfa, berseen, sugar beet, cotton, sunflower, zvheat, soybean, sugarcane, maize, flax,
Addition of Organic Matter
Addition of organic matter in larger amounts help increase soil permeability through root action, promotion of soil aggregation and release of carbon dioxide during respiration and decomposition that dissolves lime.
Application of Chemical Amendments
Chemicals such as gypsum, sulphur, sulphuric acid and hydrochloric acid may be added to salt-affected soils. These amendments lower the soil pH, react with soluble carbonate, and replace exchangeable sodium.
Reclamation of Saline Soils
The saline soils are reclaimed by applying excess water to the soil surface. This can be done by continuous ponding of water on the soil surface or by intermittent leaching. Jn Pakistan intermittent leaching is practised because ponding of •water is not possible because Of availability of insufficient water. During reclamation some kind .of vegetation suitable to wet CO rtditions and moderately tolerant to salts may be grown. Crops like rice, sorghum, berseen and kallar grass can be grown.
Reclamation of Sodic and Saline-Sodic Soils
Resematon of sodtc and saline-sodic soils is more difficult, time-consuming ane as compared to saline sods. It invotves leaching of soluble salts and replacement exchangeab:e sodium with calcium and improvement of physical properties of the soil.
- megaton water with an optimum composition and concentration of salts, of calcium, may be selected. Generally the leached water should contain a -e of soerum. The canal water without the application of amendment may not be peece, eachng especia\ty in soil which does not contain gypsum, since the removal of usec excess sas from such soils may lead to formation of sodic soils, increase in pH, and dspers;o.n of soil particles with a resultant decrease in soil permeability. Use of high_sat is effective in slowly permeable sodic and saline-sodic soils. It has also proven erectave for reclamation of sodic soils without adding any amendment.
Depending upon the characteristics of the salt-affected soils, The soil used durng reclamation of sodic and saline-sodic soils are: soluble calcium saps (cacum chloride and gypsum), acids or acid formers (sulphur and sulphuric hydrochior:c acid, iron sulphate, aluminum sulphate, and lime-sulphur), and calcium salts solubility such as by-products of lime from sugar factories. Amendments are usua!y spread on the soÆ surface and mixed with top 8 cm layer. With gypsum and acid chemicals, leeching can be started immediately, however with sulphur and lithe-sulphur, which have to be oxidized by microorganisms, a period of two or more weeksshould be allowed before leaching is initiated.
Management of Salt-Affected Soils
The ability to reclaim salt-affected soils is limited by certain factors such as insufficient supply of canal water, high cost of amendments, low permeability of soil, shallow ground water table, and use of saline ground water. Therefore, it becomes necessary to adopt management practices for profitable agriculture. This can be done by use of mechanical. and agronomic practices that help decrease the harmful effects of soluble end exchangeable sodium ions on crop plants. The management practices include:
The salt-affected soils adversely effect plants during germination and seedling therefore higher than normal seed rate may be used. Similarly crop species and varie may be selected by considering relative salt tolerance.
The salt concentration restricts plant growth by increasing solute suction, and causes water deficit even though the soil is still wet, therefore saline soils may be irrigated heavi!y than non-saline soils. The soil may be irrigated before planting to leach salts from r zone. Also irrigation water may be applied more frequently during germination, emergen and seedl:ng stages. Similarly, the soils may be irrigated heavily after light rains since th may wash salts from the soil surface into the root zonie.
Special Tillage Practices
Vanous tillage practices are applied for growing crops in salt-affected soils- These
Seedbed preparation in salt-affected soils is more important because plants are very susceptible to salt injury during the germination and ,seedling stages. Ridging of sod for seedbed preparation is the most widely adopted tillage practice for grovang crops on salt-affected soils, A fairiy high ridge is thrown up with a bank sloping to the irrigation furrow, After irrigation, a zone of salt accumulation appears on the side of ridge above the level of water in the furrow. The seeds are then planted on the side ridge below the zone of salt accumulation,
The sodic soils are high in exchangeable sodium ions, These may be tilled wth great care since these are susceptible to pudding. Cultivation of wet soils may be avoided to eliminate puddling. Deep ploughing help to improve permeability of sodic sons Deep ploughing help break impermeable layers in subsoil and provide a deeper root one for growth and better water penetration,
Sodic soils can be improved with gypsum application which improves the soil structure and results in yield increase, Saline-sodic soils can be treated with superphosphate that contain phosphorus that help reclaim these soils.. Similarly calcium nitrate may be used as source of nitrogen instead of urea, ammonium sulphate and ammonium nitrate in saline- sodtc soils,