Saline Water's Effect on Plant Growth

Soil Salinity

• Land doesn't have to be near an ocean to have saline soil. The Colorado State University Extension says that 980,000 acres of Colorado's semi-arid irrigated farm lands are adversely affected by high salinity. Desert and semi-arid soils contain excess mineral salts that are soluble in water, including the compound sodium chloride, or table salt. The salts may come from the weathering of mineral rocks or irrigation with slightly saline water. The U.S. Geological Survey says the ratio of salt to water in fresh water is less than 1,000 parts per million. In contrast, slightly saline water contains up to 3,000 ppm.

Poor Filtration and Rainfall

• Water often filters poorly in desert and semi-arid soils, because they have a high concentration of clay and silt that are difficult to penetrate. To further exacerbate the problem, the shortage of rainfall in these areas makes it difficult for salt to leach away from plant roots. So saline soils develop, and either discourage or kill plant growth.

Plant Damage

• Salt-sensitive plants are called glycophytes. Most crop plants fall into this category and grow poorly in saline soils. Plants may look fine, but still be negatively affected when absorbing too much salt, because they have to expend nutrient energy to drink enough water to balance their salt content. Salinity also makes it difficult for glycophytes to absorb water. The process of osmosis allows their roots to absorb fresh water easily, but limits absorption when water is salty. So the plants become water-starved. Salty soil further diminishes moisture by sucking water out of plants in an effort to neutralize its salinity. The Mad Sci Network website suggests placing a peeled potato in a jar of salty water to demonstrate this reverse osmotic process. The potato should begin shriveling in a few hours.

Salt Tolerance

• Plants that are salt-tolerant are called halophytes, after the mineral halite, which is rock salt. Some, such as mangroves, thrive in the ocean, while others do well in highly saline land soils. They can tolerate the salinity due to a variety of adaptations, such as secreting salt through leaf glands, storing it in parts of the plant that eventually shed, and avoiding its absorption through salt-deterring membranes in roots.

International Problem

• An overabundance of salt in soil harms crop production and can result in food shortages. Britain's Society for Experimental Biology notes that in some countries, 50 per cent of irrigated lands have become unproductive for crops due to salinity. So scientists are researching ways to adapt the traits of salt-tolerant plants to crops, such as developing roots that "just say no" to salt.