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Soil Salinity and Sodicity

soil, sampling, salinity, sodicity

Submitted by Craig Askim, Extension Agent, Agriculture and Natural Resources

Soil salinity and sodicity are major soil health related challenges facing North Dakota farmers. It is very important to understand the nature of these two different problems to manage them for healthy and productive soils.

We use many names, like saline-spots, alkali-ground, sour-ground or salt-land, but there are actually two different problems; soil salinity and soil sodicity.

Saline soils have excessive water soluble salts which don’t allow the plant roots to absorb soil water even under wet conditions, resulting in drought- stressed plants. Soil salinity is determined by analyzing soil electrical conductivity.

Sodic soils have excess sodium adsorbed (or attached) to their cation exchange sites the negatively charged particles in clay and humus that attach to positively charged plant nutrients like calcium, magnesium and potassium. Sodium is difficult to leach. This excess sodium damages soil structure by disintegrating soil aggregates and forming a hard crust or sealing of soil layers, leading  to  poor  soil  drainage,  soils which are difficult to till, poor seed germination, poor root growth and the potential for wind and water erosion.

The main source for excessive salts and sodium in North Dakota is under- lying sodium-rich shale.  The main carrier of excessive salts or sodium to the soil surface is groundwater. In this article the term ground- water is used only in reference to the zone of soil or sediments saturated with water closest to the soil surface. Groundwater can move upward to the soil surface either as shallow water- table levels or as capillary rise, especially under drier weather conditions.

Management should involve a mix of mitigation practices combined with preventive measures to stop the future spread. Mitigation of saline soils starts by managing the shallow water- table level and improving soil drainage. First, intercept any surrounding water seeps (by planting crops like alfalfa) which may contribute to a high water- table. Moderately high water-table levels can be controlled through continuous cropping with deep-rooted and late-maturing crops.

Sodic soils require the application of calcium supplements to displace the excessive sodium from the soil cation exchange sites and release it to the soil water. A common example is gyp- sum (CaSO4) added to soils with high chloride levels, or calcium chloride added to soils high in sulfates.

Once established these problems do take some time to remedy but they are manageable.

For more information please use the following link, http://www.ag.ndsu.edu/ langdonrec/soil-health.

Source: Naeem Kalwar, NDSU Extension Soil Specialist, Naeem.Kalwar@ndsu.edu

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