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This article was written by Menachem Dinar
Background
The use of saline water for agricultural practices has expanded significantly in the last decade and it is currently generally accepted that around 10% of irrigated areas are affected by salinity.
Growing under saline conditions has become an important issue not only in arid areas, but also in non-traditional "saline water areas" such as Europe and other regions, where the scarcity of water is becoming a worrisome issue.
The negative effect of saline water can be summed up in 3 main aspects:
- Osmotic effects which limit water uptake by the plant
- The effect of specific ions (e.g. Boron)
- The effect of various minerals (e.g. Na) on soil characteristics
Plant response to increasing osmotic potential in the soil solution is expressed in various negative phenomena. This includes: reduction of water uptake by the plant, decrease of transpiration and stomata conduction rates, decrease in leaf area, negative affect on root development and more. It can be generally said that the cost effectiveness of growing "commercial crops" under saline water has improved significantly over the last few years.
A wide range of technologies and systems from various disciplines provide new possibilities for cost-effective cultivation of commercial crops. They include:
1. Expansive Database
Various data on crop sensitivity, soil and water classification is available for users in the initial steps of project establishment and for choosing growing procedures. Easy access to topical information is widely available. However, as new technologies are continuously being developed, mainly in the field of genetics and Fertigation, it is important to note that the relevant data must be carefully analyzed.
2. Cost of Desalination
Technologies such as reverse osmosis are becoming more economical for agricultural practices (mainly for greenhouses). The use of a solution of saline water and high quality desalinated water, mixed by mixing valves, has become common practice in various locations.
3. Genetic Plants Resistant to Saline Water
Usage of genetic plant materials tolerant to saline water is a key factor for commercial success. Halophytes plants which are grown on small-scale areas offer an extreme example. However, using resistant grafting material, crops and/or varieties tolerant to saline water is practiced on a large scale. Genetic variation is observed even in strawberries, which are considered to be very sensitive to saline water, with diverse varieties responding differently to water salinity.
4. Cultivation and Growing Technologies
Cultivation technologies have a significant effect on cropping under saline water and include many aspects of general cropping processes, which result in a general improvement of the Soil:Water:Plant relationship.
- Soil Permeability - adding chemicals to improve soil permeability. Normally SAR values are used to determine the use of Ca in the case of high sodium content, or the use of acid in extreme cases.
- Irrigation Method - appears to have a major influence on the option of using saline water successfully. The use of a drip irrigation system enables the use of a relatively high saline level in irrigating crops considered to be relatively sensitive to salinity (e.g. potatoes).
- Irrigation Scheduling - probably a key factor in growing under saline water conditions. Scheduling irrigation will affect root development, which appears to be a major goal in the success of the crop. Frequent irrigations to reduce osmotic water potential in the near proximity of the root environment are accepted irrigation procedure.
- Other Irrigation Activities - such as leaching, planting configuration procedures and water application during rain are practical procedures used in many growing areas to reduce salinity hazards.
- Fertilization Procedures - takes water salinity status into consideration; the interaction between Cl / NO3 will affect the fertilizer formulation.
- Salinity Monitoring -of the soil solution by extractors is a simple practical procedure that follows the salinity accumulation pattern during the growing season. This procedure allows growers to adjust their irrigation program according to on-line data measured in the field. Monitoring and controlling the EC in the soil solution is also a practical procedure for improving quality parameters in some crops. Increasing the EC to a high value of 3.5 dS/m, which is considered damaging to sensitive crops, is used in common growing procedures to improve quality in various crops (e.g. processing tomatoes' dry matter production).
5. Greenhouse Growing Technology
These technologies usually face several aspects of salinity that include:
- Growth controlled by EC regulation is used in young plant production and under low light conditions. However, it is extremely likely that where water used in some instances is common practice, it may be considered harmful in other cases.
- Recycling the irrigation water in greenhouses is becoming widespread where soilless media are used. Whenever the water source quality is poor, it is expected that salinity will accumulate in the irrigation solution during the growing period. Over 3 years of intensive research, it was documented that very intensive irrigation scheduling delivered good economical results in peppers, tomatoes and roses. This is most likely due to the effect on water potential in the surface close to the root system.
Conclusion
Observations over the last decade show significant economic improvement in using saline water for irrigation. The combination of genetic and plant physiology with agro-techniques are the main components that lead to the success of cost-effective usage of saline water for irrigation.
 Download PDF version: Saline Water for Irrigation
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