Soil Salinity and Toxicity

Soil salinity management and consequent toxicity is synonymous with leaching and leaching of salts.

Most of the problems arising from excessive salinity are as explained in the previous entry physiological water deficit, due to osmosis between the roots and the soil. But there is another problem that has a negative influence on plant development, the toxicity. Excess salts in the rooting horizon of a soil are a trigger for problems for the vegetation cover.

Given that salts are soluble, problems can generally be avoided if abundant irrigation is carried out in the driest periods, not to cover evapotranspiration, but to encourage the movement of salts to deeper soil horizons where they do not interact with the canopy tissues. It should always be borne in mind that no more volume should be irrigated than the hydraulic conductivity of the soil to avoid run-off and to ensure effective flushing.

The water deficit is not the only problem when the level of salts in the soil is too high.

Excess accumulated salts have a high risk of toxicity to the crop.

• The Sodium is an element present in all soils and water in some concentration. irrigation is not found in values above 70 mg/l. It is absorbed by both roots and leaves and can cause, apart from problems of soil structure and nutrient sequestration, the burning of the tissues with which it comes into contact. Although it may not seem obvious, both tolerant and sensitive species can suffer from sodium burn during the summer season, as short, frequent irrigations are normally carried out, which encourages accumulation.
  To combat sodium accumulation in the soil, gypsum or calcium sprayed amendments are needed, which are very effective but slow to work. In our entry on the SAR and the PSI The effects are discussed in more detail.
• The Chlorine is a very reliable indicator of the processes soil physico-chemicals and can be used as an indicator for the soil salinity due to their drought-tolerant nature. Lawn grasses are not particularly sensitive to chloride and can tolerate levels of up to 100 mg/l, although they may suffer damage when watered with water containing > 355 mg/l of chloride. Some ornamental plants are sensitive to chloride concentrations exceeding 70 mg/l. When chloride is absorbed by the roots, it reduces the effective production of chlorophyll, causing its green colour to fade and reducing its ability to recover.

All elements are susceptible to cause phytotoxicity if appropriate values are reached. The values given were obtained from the Duncan, R.R., R.N. Carrow, and M. Huck. 2000. "Understanding Water Quality and Guidelines to Management. USGA Green Section Record. September-October, pp. 14-24.

• Toxicity due to Boron is rarely taken into consideration even if it is of importance. For some ornamentals at concentrations as low as 1 to 2 mg/L in irrigation water, toxicity may be present. Symptoms develop which appear as necrosis at the margins of older leaves. In comparison, grasses are more tolerant to boron and are able to thrive in soils with boron concentrations of 10 mg/kg. However, one has to be very careful if the irrigation water has boron concentrations above 2 mg/l.

Other salts that can cause toxicity are described in more detail. All values are expressed in mg/l.

Electroconductivity meters are the most effective instruments to handle correctly, our favourite is the FieldScout Soil and Water EC MeterThe salinity of the soil can be determined very precisely and economically.

Other instruments such as the POGO or the TDR allow these measurements to be made with the addition of humidity measurement.