If you see white surface crusting in areas of your fields, or if you see some areas that are wetter than others after a few days of rain, this could be an indication of a salt-affected soil. The very first step to managing salt-affected soils is to understand and identify them.
Soils containing high concentrations of soluble salts will interfere with normal growth and development of salt-sensitive crops. Such soils are called saline soils. Plants grown in these soils often appear drought stressed even when adequate water is available because the osmotic potential of the soil prevents the roots from taking in water. These areas often remain wetter compared to the rest of the field, and they usually have a white surface crust when dry.
Normal productive agricultural soils have electrical conductivity values of less than 1000 µmhos/cm, whereas saline soils have a value greater than 4000 µmhos/cm, which is equal to 2640 ppm total soluble salts. If these areas are cultivated more frequently, it can cause soil compaction and poor yield, particularly in years when rainfall is less than normal.
Soils in which the cation (positively charged ion) exchange sites are occupied by more than 15 percent of sodium and have a pH of 8.5 or above are called sodic (alkali) soils. Sodium in the soil disperses clay and similar soil particles, and prevents them from aggregating. These dispersed particles become easily suspended in water and plug soil pores. This creates poor drainage for sodic soils, which causes them to have dry subsoil and a wet surface layer. Even with adequate rainfall or irrigation, crops may fail due to these factors.
Saline-sodic (saline-alkali) soils are soils which contain greater than 4000 µmhos/cm and exchangeable sodium percentage (ESP) greater than 15. These soils have the same features of saline soils and become sodic when salts are leached out if reclamation procedures don't include gypsum. Many salt-affected soils are saline-sodic since the primary soluble ion is Na+.
The possible causes for salt-affected soils could be poor drainage, saline or sodic subsoil exposure due to erosion, parent soil material, use of high salt irrigation water, long-term use of some fertilizers, low rainfall or oil field activity.
The following techniques or events can help reclaim saline soils.
- Salt can be leached out of the root zone through good quality irrigation water or by heavy rainfall.
- Create good surface and internal drainage. The use of tile drains and open ditches in the fields can increase drainage and remove some of the salts.
- Break the compacted layers that occur near or at the soil surface.
- Add organic matter, such as rotted hay or feedlot manure, at 10-15 tons/acre to improve soil porosity.
There are some additional considerations in the reclamation of sodic and saline-sodic soils.
- Reclamation of sodic soils is similar to saline soil in leaching the salts out of the root zone, except that gypsum should be added to remove the sodium. The amount of gypsum required depends on the soil texture and ESP.
- Reclamation of these salt-affected soils is a very difficult thing and can take several years, so be patient.
- Sandy soils in high rainfall regions can be reclaimed more easily than clay soils if rainfall is the only source of reclamation.
Apart from these, other management practices can be followed. They include avoiding excessive fertilization after the leaching of salts process has started, avoiding deep tillage as it might bring salts to the soil surface (forcing a restart of the reclamation process), establishing a cover crop to prevent erosion, and other management practices that will reduce surface evaporation and encourage water movement downward in the soil. Some crops are more salt- tolerant than others and should be considered in these situations.