Salinity Levels of Water Suitable for Agriculture
The suitability of soil for agriculture depends on the salinity levels it contains, as plants respond differently to salinity. The classification of water salinity levels extracted from the soil is shown in the table below:
| Dissolved Salt Concentration in Water Extracted from Soil (g/L) | Soil Salinity Level |
|---|---|
| 0-3 | Non-saline |
| 3-6 | Slightly saline |
| 6-12 | Moderately saline |
| >12 | Highly saline |
Salts limit plant growth in soil by reducing the amount of water absorbed by roots and may also have toxic effects on plants. Since some plants tolerate soil salinity better than others, the classifications based on their tolerance are as follows:
Plant Sensitivity to Soil Salinity
Low Salinity Sensitivity
- Dates
- Barley
- Beets
- Cotton
- Spinach
Moderate Salinity Sensitivity
- Wheat
- Tomatoes
- Oats
- Rice
- Corn
High Salinity Sensitivity
- Red clover
- Peas
- Sugarcane
- Apples
- Potatoes
Other plants such as almonds, carrots, cucumbers, and grapes exhibit varying degrees of sensitivity to salinity depending on their type and growing conditions.
Impact of Salinity on Agricultural Production
Salinity negatively affects crop, pasture, and tree production by hindering nitrogen absorption, plant growth, and reproduction. Salts with toxic concentrations, such as high chloride levels, pose additional threats to plants.
Key Effects Include:
- Osmotic Stress: Reducing the plant’s ability to absorb water.
- Leaf Damage: High salt uptake can cause leaf tip burn.
- Root Desiccation: Leading to root damage and production decline.
- Early Sensitivity: Plants are generally more sensitive to salinity during germination and early growth stages.
Solution: Addressing soil salinity is critical to increasing agricultural yields and protecting plants from these adverse effects.
Measuring Salinity
Soil water salinity is measured by passing an electric current between the electrodes of a salinity meter in a soil or water extract sample. The electrical conductivity (EC) is then calculated, with higher conductivity indicating higher salt concentrations, as salinity and conductivity are directly proportional.
Causes of High Soil Salinity
Several factors contribute to the rise in soil salinity:
- Rock Weathering: Salt fragments resulting from chemical and physical processes in rocks entering water streams and groundwater reservoirs used for irrigation.
- Salt Dissolution: Dissolving salts from rocks, such as feldspar and carbonates, during groundwater seepage.
- Evaporation: Increased evaporation rates and decreased rainfall.
- Coastal Winds: Transporting salts from shorelines to water bodies and soil.
- Human Mismanagement: Overuse of irrigation water and groundwater.
- Poor Drainage: Waterlogged soil without proper drainage for prolonged periods.
Proper management of water resources and soil conditions can help mitigate the effects of salinity on agriculture.
