Salinity is a global problem. The continuous loss of arable land due to irrigation in arid and semi-arid regions of the world, over-exploitation and mismanagement contribute to global change in a way which currently appears to draw much less concern in the media and the general public than the accumulation of green house gases –carbon dioxide, methane and others – in our atmosphere and putative temperature increase and climate changes associated with them. Nevertheless, the advancement of desertificaton by salinization and its threatening of global agriculture can be readily quantified.
Agricultural losses caused by salinity are difficult to assess but estimated to be substantial and expected to increase with time.Secondary salinization of agricultural lands is particularly widespread in arid and semi-arid environment where crop production requires irrigation schemes. At least 20% of all irrigated lands are salt affected with some estimates being as high as 50% whereas the world's population continues to rise, the total land area under irrigation appears to have levelled off.
Salinity is one of the most severe environmental factors limiting the productivity of agricultural crops. Most crops are sensitive to salinity caused by high concentration of salts in the soil. The cost of salinity to agriculture is estimated conservatively to be about US$ 12 billion a year, and is expected to increaseas soils are further affected (Ghassemi et al., 1995). In addition to this enormous financial cost of production, there are other serious impacts of salinity on infrastructure, water supplies, on soil structure and stability of communities. Responses to salinization have been of many general kinds;engineering the environment to manage increased salt in the soil irrigation anddrainage management; by "engineering" the plants to increase their salt tolerance. Salt tolerant plants may also ameliorate the environment by lowering the water table in salt affected soils.
Salinization commonly occurs as an outcome of agricultural practices, either associated with irrigation or due to long – term changes in water flow in the landscape that can follow land clearance or changed water management. Salinization associated with agriculture occurs when salts build up in the root zone, either because the soil is intrinsically saline, or because the drainage of water from the sub-soil is not sufficient to prevent saline waters rising into the root zone. It therefore tends to be common in arid and semi-arid regions where leaching of salt is poor due to lower rainfall; where there are strongly saline sub-soils formed from marine deposits or where irrigation changes water tables and salt flow.
Saline soil refers to a soil that contains sufficient soluble salts to impair its productivity. Similarly, alkali soils can be defined in terms of productivity as influenced by exchangeable sodium. So,alkali soils may or may not contain excess soluble salts.
The soluble salts that occur in soils consist mostly ofvarious proportions of the cations sodium, calcium and magnesium, and the anions chloride and sulphate. Constituents that ordinarily occur only in minor amounts are the cation potassium and the anions bicarbonate, carbonate and nitrate.
Salinity is a major threat to irrigated agriculture because many of the soils and irrigation waters contain significant amount of dissolved salts. Due to excessive evapotranspiration in arid and semi-aridregions, the secondary salinization is becoming important factor for salinity.
Vijayvargiya, S. and Kumar,A. (2011): Inluence of Salinity Stress on Plant Growth andProductivity:Salinity stress influences on plant growth. Germany.Lap Lambert Academic Publishers.170 pp.