Testing solutions for salts in soil and water.

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Testing solutions for salts in soil and water.

Conductivity is an easy qay to measure salts in water. There are several electronic conductivity testers available that will test conductivity in drinking water, stock water, irrigation water or even nutrient solutions. The Hanna Instruments HI98311 DiST 5 Conductivity tester is a good example. This tester measures conductivity in the range 0 to 3999 microS/cm which makes it suitable for testing drinking water, irrigation water and nutrient solutions. The things to look for in a tester are; is it waterproof and is it easy to calibrate? The DiST 5 is good for outdoor use in harsh or wet conditions. All testers need to be calibrated every so often to make sure they are reading accurately. The DiST 5 uses a 1413 microS/cm calibration solution and calibration is as easy as pressing buttons. Conductivity will not tell you the proportion of different salts that are present. It will just give an approximation. This can work because it has been found that for different types of water the conductivity is related to Total Dissolved Salts or TDS. This is a physical measure of salts in parts per million or ppm. It is OK to say mg/L in solutions instead of ppm as it makes more sense. For relatively fresh water to get TDS, multiply conductivity by 0.67. In salty or brackish water use 0.55 instead. Its just an approximation but useful. The DiST 5 has an inbuilt calculator to give TDS as well as conductivity. The user can set the TDS factor. To read more about conductivity and TDS please see Measuring salinity.

Testers like the DiST 5 can be used for testing salts in the soil solution as well. First a soil sample has to be mixed with a known volume of distilled or RO water to give enough sample to test. This is a good way to find out if the water that feeds your plants or crop, the soil solution, is becoming too salty. Instructions on how to do this are in the spreadsheet file Soil conductivity calculator. The spreadsheet does all the calculations once you have put in how much soil and water were used and the tested conductivity.

Read more about the DiST 5 tester at DiST 5 conductivity tester.

A convenient conductivity meter for testing both soils and water is the Hanna Instruments HI993310 Dual soil / liquid. This meter has two probes, one for liquids like irrigation water and the other a tough pointed probe for direct in-soil conducivity in the soil solution. This meter has a wide conductivity range, up to approx 20,000 microS/cm.

Read about the dual soil / liquid conductivity meter at HI993310 Dual soil / liquid meter.

In irrigation water it is important to find out what the balance is between the desirable salts like calcium and magnesium and and the undesirable salts like sodium and chloride. Calcium and magnesium can be measured in irrigation water using the Hanna Instruments HI38035 Calcium and Magnesium kit. Read about this kit at calcium and magnesium kit. Chlorides are also relatively easy to measure using a kit. A suitable kit is the Hanna Instruments HI3815 dual low range chloride kit. Read about this kit at Dual low range chloride kit. Sodium is harder to measure and there are no simple kits. At Apps Labs we find the easiest way is to use a sodium specific electrode. In the lab this is OK because there are calibration solutions and tricky calculations to deal with to get a result. For everyday folks this is not an easy option. Best send a sample to the lab to be tested!


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