HOW DOES SALINITY INFLUENCE SOILS?

Electrical conductivity (EC) is the capacity of a substance or material to allow the passage of electric current and is generally expressed in dS/m (dS=deciSiemens). La EC is proportional to the concentration of salts in solution and is the most commonly used parameter for measuring salinity.

It is essential to control the EC in the soil, as when irrigating, part of it infiltrates and another part is retained by the soil, contributing salts to it. Irrigation water and fertilisers incorpórate salts into the soil, which can undergo a salinisation process. A soil is considered saline when it has an EC higher tan 4 dS/m in the saturated extract. The presence of salts affects soil structure, nutrient assimilation by the plant and soil microbial activity.

Salinity tolerance is the ability of the crop to withstand soil salinity without experiencing detrimental effects on its development and production. It is only when salinity reaches a certain level (or threshold value) that the increase in salinity begins to cause a progressive decrease in production.

The table shows the threshold EC (dS/m at 25 ºC) of the saturation extract of soil (ECs) and irrigation water (ECa) estimated for different crops in the mature state. Values higher that those indicated may result in yield losses of more tan 10%, although other parameters such as climatic variables, soil properties and type, variety, etc., must be taken into account, as they may cause the values indicated to vary and should be taken as a reference.

Salinity affects the crop’s water absorption capacity, photosynthetic performance (stomata closure), chlorosis and leaf necrosis, and even toxicity. It is therefore very important to control EC using fertigation techniques, and to parameterise soil variables such as Volumetric content and EC by means of sensors.