Copy
Salt accumulation tends to occur in environments with low rainfall, high evapotranspiration rates, and/or a source of water that transports salts to the root zone. High concentrations of salts in the rooting zone can cause plant osmotic stress, toxicities of specific salts, or soil physical degradation.
Sodium, magnesium, chlorides, and sulfates are a few examples of common salts that can appear in soils (though their forms may vary).
A key management technique for saline soils is to rotate with, or switch to, a salt-tolerant crop. For instance, corn is considered to have a low salinity threshold (as measured by the electrical conductivity [EC = dS/m] of the soil) with a moderately sensitive rating, whereas barley has a high salinity threshold with a high tolerance rating. Switching from corn to barley provides an opportunity for crops to be more productive on salt-affected acres.
Economic considerations can help determine an acceptable yield reduction or the choice to switch from crops with low salt tolerance to crops with high tolerance.
Avenues for salt removal, in the absence of irrigation, are limited in areas with low precipitation rates as soil salts accumulate when they are not “flushed” out of the root zone by rainfall or snowmelt (leaching). Salt accumulation is not common in high precipitation areas because natural precipitation removes salts from the soil system through leaching. This substantially lowers the risk of salt injury and the impact that salinity can have on yield in high rainfall areas.
Water sources can impact and/or cause soil salinity. Water sources that are rich in salt can increase soil salinity both during application and over time as salt is added and accumulates in the soil. Periodic water-quality analyses can help identify the salinity load applied from water sources.
Irrigation water can also be an important contributor to soil salinity. Both ground and surface waters often contain some level of soluble salts. Irrigation water can introduce salt to soil systems that will accumulate if they are not removed. Any salt contained in the water will be concentrated in the soil through evaporation if not removed by periodic leaching.
Excess irrigation can be a key remediation practice in removing salts from the soil through leaching and can be augmented with subsurface soil drainage.
Compost, manure, and fertilizer may be sources of salts added to soil. The type of salts and concentration of salts added in these materials should be considered if the risk for salt accumulation is present. In most cases, fertilizers are simple salts that provide key nutrients to crops. At normal fertilizer application rates, salt contributions are generally insignificant compared to native soil salts or salts supplied by waters. Fertilizers with high salt indices should be avoided if saline soil conditions exist. Applying high rates of manure can also contribute significant salts to the soil and must be managed accordingly.
Soils with high evaporation rates and low precipitation are more likely to accumulate salts. As water evaporates from the surface, salt deposits are left behind resulting in increased salinity.
Under certain conditions, groundwater can contribute salts to the soil through residual salt deposits during evaporation and deposition. As groundwater levels fluctuate in the soil over the year, salt deposits are left behind.
High water tables bringing salt up into the root zone is a common cause of soil salinity.