Soil has been described as a porous medium consisting of minerals, water, gases, organic matter and microorganisms. The largest component of soil is the mineral portion, which makes up approximately 45-49% of the volume.
Some of the mineral portion consists of primary mineral particles. These are the sand and silt particles. Some of it is made up of secondary minerals that result from the weathering of primary minerals into secondary minerals, like silicate clays. This process results in the releasing of important plant nutrient ions and other elements that make up the remainder of the mineral fraction. The ions attach to the soil clays and soil organic matter, or they react with other ions to form low-solubility compounds like lime (calcium carbonate) and gypsum (calcium sulfate). These compounds are correctly known as salts but are quite different from table salt (sodium chloride).
When they are present at normal levels they help to stabilize the soil particles, buffer the soil pH and serve as a source of soil nutrients. If these salts are not present in sufficient levels, nutrient deficiencies occur, soil pH is low, and soils may lack structure. The reason for soil testing is to determine the level of soluble minerals in the soil so the ones in short supply can be added as fertilizers or other amendments. If certain elements are present in very high levels there may be problems with the availability of other elements due to competition or insolubility. Excess of other elements can lead to toxicity, high pH — or in the case of sodium — destabilization of the soil’s structure. If the concentration of all salts is too high their presence can hinder plant growth because the ions compete with plants for water. A soil conductivity test is used to determine the extent this is happening.
Soils that are very low in minerals under native conditions are usually also low in organic material. These soils require very large additions of fertilizers and other amendments like lime to make them suitable for crop production. Even when this is done, it is difficult to maintain productivity because the nutrients are easily lost. Similarly, soils that are very high in salts under native conditions are extremely difficult to convert to crop production without using extraordinary measures.
Consequently, most of the soils that have been converted to crop production began with moderate levels of "salts." It is common for fields that have been cropped for long periods to experience issues with managing mineral elements. Many times the result is loss of nutrients due to leaching, erosion or transport from the field in grain or biomass. This leads to lowered pH, soil structure degradation and the need to add large amounts of lime, fertilizers and other amendments. In some cases cropped soils begin to develop saline seeps.
Some saline seeps develop as a result of excess water due to improper management of the water cycle by the land managers. Other times off-site influences like road and drainage ditches, shelterbelts, ponds (man-made or natural) and/or mismanagement of the water cycle by neighboring property owners can also result in the development of saline seeps. One of the main sources of excessive salinity issues in agriculture is irrigation because it adds salts in the irrigation water to those in the soil.
It is important for landowners to act quickly when they suspect their land is being adversely impacted by salinity. The first step is to do a thorough job of sampling the soil in the field to determine the location, degree, type and extent of the problem. Using Web Soil Survey to identify the soil types and topography of the field will be helpful. Obtain help from NRCS or SDSU Extension personnel staff in interpreting the results. It is important to determine why the problem is occurring before trying to find a solution.
One thing is certain, adding more salts (gypsum or other amendments) to a soil that is already impacted by salt is not the correct approach. You need to figure out what is going on before trying to solve it. There are no one-time answers.