Overview
This lecture explains soil salinity testing, focusing on the saturated paste method and comparing it to other extraction techniques.
Saturated Paste Method
- The saturated paste method mixes soil and water until the soil is saturated, matching conditions near plant roots.
- Soil is mixed with water until it glistens, falls off a knife, and holds its shape without excess liquid.
- For clay soils, allow the mixture to sit overnight so clays can absorb water fully.
- The next day, adjust as needed, extract the liquid using suction, and measure salinity with a salinity meter.
- This method best represents the plant root environment after irrigation and is the standard for developing plant salinity response data.
- Though time-consuming and subjective, it provides more accurate results for management decisions.
Alternative Extraction Methods
- The 1:1 extract uses equal amounts of soil and water (e.g., 25g soil and 25mL water), producing EC 1:1 results.
- The 1:2 and 1:5 extracts use one part soil to two or five parts water, respectively; these are common in various labs worldwide.
- All alternative methods involve letting the mix sit, extracting the water, and testing for salinity.
- These methods may not correlate as strongly with actual plant responses as the saturated paste method.
Importance of Method Selection
- Plant response data and salinity management practices are based on the saturated paste method.
- Using the saturated paste method at least once establishes a reliable baseline for salinity management.
Key Terms & Definitions
- Salinity — presence of dissolved salts in soil.
- Saturated Paste — a soil-water mixture at saturation, simulating root-zone moisture conditions.
- Electrical Conductivity (EC) — a measure of a solution's ability to conduct electricity, indicating salt concentration.
Action Items / Next Steps
- Perform a saturated paste test for initial soil salinity assessment.
- Use test results to inform soil management decisions.