Dealing with saline soils is one of the most challenging problems in crop production both locally and globally. A recent report by the FAO with information from 118 countries shows that more than 424 million hectares (more than 1 billion acres) of topsoil and 833 million hectares (more than 2 billion acres) of subsoil are salt-affected. It is estimated that more than 5 million acres in the Canadian Prairies are impacted by some degree of salinity. With the current challenge of feeding a growing population with limited agricultural land, finding solutions that can improve crop productivity in saline soils is critical.
What causes soil salinity?
Soil salinization occurs when water-soluble salts accumulate in the soil. This usually happens due to a combination of several factors: the parent rock from which the soil is formed is rich in soluble salts, there is a high water table, a high evaporation rate and a low annual rainfall. Generally, if the water table is within two meters (six ft.) of the soil surface, capillary movement will carry water and dissolved salts to the surface. And if evaporation exceeds infiltration, the salts will remain in the upper layers of the soil where they can negatively affect plants.
How saline soils affect crops
Excess salts make it difficult for plants to take up water. This is because water moves into plant roots through the process of osmosis which is influenced by the difference in the salt levels of the soil water and the water contained in the plant. If the salt level of the soil water is high, water will move from plant roots to the soil instead of from soil to plant. With time, the plant will become dehydrated, growth is limited, and the plant might die. In salt-affected soils, seed germination will be poor because of low imbibition of water and salt toxicity.
Lab experiment on the effect of salinity on canola growth. Soils in the red pots were made saline by adding sodium chloride (table salt) which affected germination and growth
How to detect salt-affected soil
Saline patches in a field are often characterized by poor crop growth. For very salty soils, a whitish precipitate of salt may appear on the soil surface, especially after a long dry period. Some salt-loving weeds such as Russian thistle, Kochia and foxtail barley may also colonize the area. A routine soil test can more accurately identify the level of salinity and what kinds of salts are present.
What are some solutions to improve crop productivity in a saline soil?
Reclaiming saline soils can be difficult and expensive. Reclamation methods usually involve installing drainage and then leaching the excess salts out of the soil using sufficient rainfall or irrigation. In dryland farming, this may not be practical or economically viable.
Therefore, efforts are being directed towards more feasible alternatives. Breeding salt-tolerant varieties and developing seed treatments that help plants overcome stressful conditions are two options that are available to improve crop productivity in saline soils. A good seed treatment can complement breeding efforts and boost plant health in the early stages. Moreover, several microorganisms, phytohormones and biostimulants have been shown to enhance plant defense mechanisms and help crops thrive under abiotic stresses such as salinity. These can be incorporated into a cropping program either at seeding or as foliar applications during the season. Variable rate application of fertilizer is also useful to ensure that input is allocated to more productive areas and that saline areas are not further salinized by too much fertilizer. Long-term management of saline areas may also involve seeding them to salt-tolerant perennials that root deeply to use up a lot of the excess water thereby reducing the upward movement of dissolved salts to the soil surface.
– Ikenna Mbakwe, PhD, PAg
Head of Research