Salt content in irrigation water
The excess of salts content is one of the major concerns with water used for irrigation. A high salt concentration present in the water and soil will negatively affect the crop yields, degrade the land and pollute groundwater.
The suitability of water reuse for irrigation with high salt content depends on the following factors:
- Salt tolerance of the type of crop
- Characteristics of the soil under irrigation
- Climate conditions. The quality of the irrigation water plays an essential role in arid areas affected by high evaporation rates and cause high concentrations of salt accumulating in the soil.
- Soil and water management practices
Special account should be taken to coastal areas where the infiltration of sea water poses a high risk of salinity in the water that is then pump from wells to be used in irrigation. For example in Spain the overexploitation of groundwater resources for agriculture lowered the water table and as a consequence caused the seawater intrusion in the coastline.
Salinity with moderate content of salts can be used if moderate leaching occurs.
Water with high saline (ECi>1.5) and sodium (SAR>6) should not be used for water irrigation. Nevertheless, in some places with water shortage, water with high salinity concentration is used as a supplement for other sources and therefore a good management and control is essential and the salt tolerance of the plants must be considered.
If water with a very high salinity is used (extreme water shortage circumstances) the soil must be permeable, drainage must be adequate, water must be applied in excess to provide considerable leaching and salt-tolerance crops should be selected.
Salinization of soils on Irrigated Lands
Source: Adapted from F.Ghassemi, A.J.Jakeman, and H.A. Nix, salinisation of Land and Water Resources (Sydney: University of New South Wales Press, 1995)
If a farmer annually applies 10,000 tons of irrigation water to a Ha of crops, which is typical, between 2 and 5 tons of salt will be added to that land every year. Unless these salts are flushed out, enormous quantities can build up over the course of years or decades.
Salt tolerance of different crops
The yield of different crops in relation with the salinity content of the water used for irrigation, depends on the type of crop, soil and environmental conditions.
Management Practices for Irrigating with Saline or Sodic Water
The following consideration should apply:
- Adequate internal drainage. This measure is intended to avoid free movement of water in the root area.
The appropriate leaching requirement depending on tolerance levels for specific crops should apply to avoid the accumulation of salt. For example if natural drainage is not adequate, a drainage system must be installed.
- Higher water availability in soil. At high salt concentrations plants will not absorb all the normally available water.
- Proper management and control of SAR and salinity controls. Ex. add soluble calcium such as gypsum (calcium sulphate) to decrease the SAR to a safe value.
Related pages:Toxic ions hazard of irrigation water