Salt-affected soils (SAS) describe both saline soils and sodic soils. Saline soils contain salts more soluble than gypsum in a concentration sufficient to negatively affect the ability of plants to take up water, while sodic soils contain high amounts of sodium ions that weaken the bond between the soil particles adversely affecting the soil’s structure. This loss of soil structure through dispersion leads to soil compaction, severely reducing the flow of water through the soil and impacts plant growth and health. Alkaline soils occur when sodic soils have a pH higher than 8.5.

Salt affected soils are a global issue

Soil salinization is a multifactorial phenomenon that can occur naturally by raising sea level or water intrusion from sea, river or groundwater, but can also be of anthropogenic origin through agricultural intensification, inappropriate management practices, and use of residual irrigation water or excessive application of mineral fertilizers. Climate change may accentuate this process and inhibit plant growth, affecting small farmers and rural communities more acutely, who have fewer means to prevent, manage and mitigate/adapt to soil salinization. These soils undergo a rapid decline of health, losing their capacity for biomass production, natural filtration, carbon sequestration and other necessary ecosystem functions. Salt-affected soils are a major global challenge and every country needs to be concerned by the consequences of salinization and sodification since the impact on the environmental services provided by soils goes beyond political boundaries.

Key data

• Over 1 100 Mha of soils are affected by salinity and sodicity, of which 60 percent are saline, 26 percent sodic and the remaining 14 percent saline-sodic.
• Salt-affected soils are found on all continents. The most affected regions are the Middle East, Australia, North Africa, and Eurasia.
• Since most of the salt-affected soils occur under arid or semi-arid climates, food production in these regions requires irrigation. Some estimations indicate that 20 to 50 percent of irrigated soils are salt-affected.
• Europe adds 1 million metric tons (109 kg) of salts per annum to the environment, while USA applies about 10 times more than this annually to paved surfaces, causing secondary salinization.

What is FAO and its GSP doing about this?

Some of the processes involved in soil salinization and sodification have been thoroughly studied, such as those related to irrigation, but others have not, and the magnitude of some of their impacts on soils are still largely unknown. 

FAO and its Global Soil Partnership are currently addressing this through a range of activities, including the recently launched International Network of Salt-Affected Soils (INSAS) and the development of the Global Soil Salinity Map and its massive capacity development programme that will provide an improved assessment of the salinity status of the world’s soils.

The Global Symposium on Salt affected Soils

Furthermore, the Global Symposium on Salt affected Soils will take place from 20 to 22 October 2021. This event is jointly organized by FAO and its Global Soil Partnership (GSP), the Intergovernmental Technical Panel on Soils (ITPS), together with the Government of the Republic of Uzbekistan, the United Nations Convention to Combat Desertification (UNCCD), the International Union of Soil Sciences (IUSS), the International Center on Biosaline Agriculture (ICBA), the International Network of Salt-Affected Soils (INSAS), and the Global Framework on Water Scarcity in Agriculture (WASAG). Farmers, extension services, NGO's, research institutes, governments and the private sector will convey virtually in order to review the status and challenges of salt-affected soils as well as their conservation and sustainable use.

Other resources

• http://www.fao.org/global-soil-partnership/itps/itps-soils-letter/en/
• http://www.fao.org/global-soil-partnership/itps/en/