By Keana Boere, AAg, Agri-Environmental Specialist, Outlook
Salts naturally occur in soil and water but can become an agronomic problem when they accumulate in the soil. Accumulation of soluble salts can occur when there is a lack of rainfall and not enough water to leach salts through the soil profile. High evaporation loss brings water and dissolved salts up from deep within the soil profile. These salts remain on the soil surface as salt crusts when water evaporates. Poor drainage and irrigation water with high dissolved salt content can also contribute to salinity problems in an area.
Salt-affected soils are classified as saline, saline-sodic or sodic. Many dissolved salt ions contribute to soil salinity, but classification of salt-affected soils depends only on the concentration of sodium ions (Na+). Soils with an electrical conductivity (EC) greater than 4 dS m-1 are considered saline.
It is easy to recognize a salinity problem in a field when the area is unvegetated and a white salt crust is visible on the soil surface. Salinity can be a problem in less noticeable areas in a field and can be identified by:
- Uneven or wavy crop patterns across the field. Salinity levels can vary across a field and some areas may be more affected than others.
- Crop growth can be inhibited by salinity, meaning low yields could indicate a salinity problem.
- An abundance of salt-tolerant weeds in an area. Salt-tolerant weeds include kochia, foxtail barley and Russian thistle.
- If soil samples are consistently taken in a field over many years, an increase in EC can be noticed on soil test results, indicating a potential salinity problem.
- Salinity levels in a field can be measured though soil sampling, electromagnetic meters (EM38), or hand-held EC probes.
Different crops have varying tolerances to salinity. Cereals are better at tolerating salinity than canola, and pulses are the least tolerant. When crops are affected by salinity, they often look drought stressed even though water is sometimes present. This is because salt ions hold tightly onto water, making it difficult for plants to access it.
Soil salinity can be difficult to manage and management options usually are not permanent solutions. Several practices can be used to manage moderate levels of salinity.
- Avoid summer fallow in rotations to reduce the amount of evaporation.
- Select salt-tolerant crops or varieties for salt-affected areas.
- Organic matter additions (manure or crop residues) improve water infiltration and water holding capacity of the soil, reducing evaporation.
- A drainage system can be used to lower the water table.
Areas with high levels of salinity are best managed by establishing salt-tolerant, perennial vegetation. Wheatgrasses, specifically the AC Saltlander variety, and alkali grasses both have high salt tolerances. Alfalfa, sweet clover and birdsfoot trefoil are legume options that have some salt tolerance as well. High salinity areas typically do not support annual crop production.
If you have questions regarding soil salinity or how to manage it, contact your local crops extension specialist or call the Agriculture Knowledge Centre at 1-866-457-2377.