History has shown that an increase in soil salinity results in a decrease in crop productivity, and ultimately, the struggles to sustain a community. One of the earliest and most major occurrences of an increase in salinity happened during 2400-1700 BC in ancient Mesopotamia, now southern Iraq. Irrigation projects were built for agricultural purposes, but the resulting increase in soil salinity left the fields so salty that they were unable to grow enough food to sustain their communities. Many of the great cities dwindled down to small villages or were left in ruins.
This same process is occurring in California, specifically the west side of the San Joaquin Valley. The San Joaquin Valley, which makes up the southern portion of California’s Central Valley, is among the most productive farming areas in the United States. However, salt build-up in the soils and groundwater is threatening its productivity and sustainability. Another example is with the Imperial Valley and the Salton Sea. Irrigation water comes from the Colorado River and is very high in salt. The runoff from irrigation water flows to the Salton Sea. With no outlet, the Salton Sea’s salinity has continuously increased as the water evaporates. According to California Agriculture Online, three factors contribute to salinization:
1. All irrigation waters contain dissolved salts, with concentrations varying considerably according to the origin of the water.
2. Plants extract negligible amounts of salt, so the soil solution becomes concentrated as water is removed by evapotranspiration.
3. Water quantities in excess of evapotranspiration must be applied to leach salts beyond the root zone to prevent reduced crop yields.
In areas where salinity poses a problem, sustainable irrigated agriculture can still be achieved. This would be by: (1) maintaining a salt balance so that salts added is equal to salts removed, and (2) removing drainage water and dissolved salts when the water table reaches the root zone. When the water table is high, water is more prone to evapotranspiration, thus increasing the amount of water depleted and leaving behind salts.
Both methods mentioned above are simply stated, yet they are far more complicated, especially when applied on a global scale. Not only are there technological and environmental factors, but there are also cultural and political factors that can hinder the salt balance within sustainable irrigated agriculture.
Letey, John. “Soil salinity poses challenges for sustainable agriculture and wildlife”. University of California. 2000. Site accessed on 25-Oct-2012. http://ucanr.org/repository/cao/landingpage.cfm?article=ca.v054n02p43&fulltext=yes
Schoups, Gerrit et al. “Sustainability of irrigated agriculture in the San Joaquin Valley, California”. University of California, Davis. 2005. Site accessed on 25-Oct-2012. <http://www.pnas.org/content/102/43/15352.full.pdf>
Written By: Stephanie Lynn, Aquaponics Intern