The Problem Of Salinization
Salinization is a major problem associated with irrigation, because deposits of salts build up in the soil and can reach levels that are harmful to crops. In addition, the salts can make ground water, which may be in use for drinking, saltier and unsuitable for drinking. It is mostly in arid and semiarid regions where the problem of high salt content deposited from irrigation threatens crops.
Drip irrigation is a technique that can be used in areas where the ground water level is high and in danger of suffering from a high salt content. Where salinization is a problem to plants, enough water can be added to the irrigation process to leach salts away from plant roots. When the danger of salinization is to the water table, it is necessary to add drainage to the irrigation system away from the water table.
Crops have different salt tolerances and their selection in relation to the salinity of the soil is an advisable practice. Among the common crops that have a high salt tolerance are red beets, spinach, kale, asparagus, sugar beets, barley, cotton, date palms, and some grasses used for animal feed, such as wild rye and wheat grass. Crops that have a low tolerance for salinity include radishes, celery, green beans, fruits such as pears, apples, oranges, grapefruit, plums, apricots, peaches, strawberries, lemons, and avocados, and a number of clovers that are used for animal grazing.
Areas in the world where farming is threatened by high salinity include the Indus Basin in Pakistan where they also face the problem of a rising water table. The Imperial Valley in California, formerly productive agricultural lands in South America, China, India, Iraq, and many other regions throughout the world are all facing the threat of losing fertile land because of salinization. After the building of the Aswan Dam in Egypt, the Nile River and the surrounding fields that had been irrigated successfully for over 5,000 years became threatened by high salinity in the water.
The main technique used to reclaim land that has developed a high salt content from irrigation is a leaching process. This is based on a careful analysis of the soil and the amount of water that must be applied to reach a level of acceptable salt content. One problem of leaching is that other nutrients needed by the crops, besides the undesirable salts, may also be leached from the soil. Consequently, nutrients often need to be replaced after an area is reclaimed from high salinization.