- Author: Ben Faber
I was just speaking to a group of Certified Crop Advisors and there was some confusion about the units used by different labs to report their results, so I put together this sheet to help understand the relationship between the different terms. They are usually interchangeable, but one needs to know how they convert between each other. So here is a cheat sheet.
Common ions in water: calcium (Ca2+), magnesium (Mg2+), sodium (Na1+)
sulfate (SO42-), chloride (Cl-), carbonate (CO32-), bicarbonate (HCO3-), boron (H3BO3)
Measured as parts per million (ppm) or milligrams per liter (mg/l), which are interchangeable , or milliequivalents per liter (meq/l). A milliequivalent is the ppm of that ion divided by its atomic weight per charge.
Example: Ca2+ with atomic weight of 40 and a solution concentration of possibly 200 ppm. Ca2+ has two charges per atom, so it has a weight of 20 per charge. 200 ppm divided by 20 = 10 meq of calcium for a liter of water.
Total Dissolved Solids (TDS): measure of total salts in solution in ppm or mg/L
Electrical Conductivity (EC): similar to TDS but analyzed differently.
Units: deciSiemens/meter(dS/m)=millimhos/centimeter (mmhos/cm)=
1000 micromhos/cm (umhos/cm).
ConversionTDSEC: 640 ppm=1 dS/m= 1 mmhos/cm=1000 umhos/cm
Hardness: measure of calcium and magnesium in water expressed as ppm CaCO3
pH: measure of how acid or base the solution
Alkalinity: measure of the amount of carbonate and bicarbonate controlling the pH, expressed as ppm CaCO3.
Sodium Adsorption Ratio (SAR): describes the relative sodium hazard of water
SAR= (Na)/((Ca+Mg)/2)1/2, all units in meq/l
1.5 feet of water with EC of 1.6 dS/m adds 10,000 # of salt per acre
and that same water with 20 mg/l of nutrient will supply 80# of that nutrient/acre
Sea water has ~ 50 dS/m, 20,000 ppm Cl, 10,000 ppm
Irrigation water WATCH OUT- 1,000 ppm TDS, 100 ppm Na/Cl, 1 ppm B
- Author: Ben Faber
Along with drought there are also concerns about water quality which has all kinds of weird units that area actually convertible. Here's a little guide for the principle water quality components and their conversions.
Water Terminology
Common ions in water: calcium (Ca2+), magnesium (Mg2+), sodium (Na1+)
sulfate (SO42-), chloride (Cl-), carbonate (CO32-), bicarbonate (HCO3-), boron (H3BO3)
Measured as parts per million (ppm) or milligrams per liter (mg/l), which are interchangeable , or milliequivalents per liter (meq/l). A milliequivalent is the ppm of that ion divided by its atomic weight per charge.
Example: Ca2+ with atomic weight of 40 and a solution concentration of possibly 200 ppm. Ca2+ has two charges per atom, so it has a weight of 20 per charge. 200 ppm divided by 20 = 10 meq of calcium for a liter of water.
Total Dissolved Solids (TDS): measure of total salts in solution in ppm or mg/L
Electrical Conductivity (EC): similar to TDS but analyzed differently.
Units: deciSiemens/meter(dS/m)=millimhos/centimeter (mmhos/cm)=
1000 micromhos/cm (umhos/cm).
ConversionTDSEC: 640 ppm=1 dS/m= 1 mmhos/cm=1000 umhos/cm
Hardness: measure of calcium and magnesium in water expressed as ppm CaCO3
pH: measure of how acid or base the solution
Alkalinity: measure of the amount of carbonate and bicarbonate controlling the pH, expressed as ppm CaCO3.
Sodium Adsorption Ratio (SAR): describes the relative sodium hazard of water
SAR= (Na)/((Ca+Mg)/2)1/2, all units in meq/l
1.5 feet of water with EC of 1.6 adds 10,000 # of salt per acre
and that same water with 20 mg/l of nutrient will supply 80# of that nutrient/acre
Sea water has ~ 50 dS/m, 20,000 ppm Cl, 10,000 ppm
Irrigation water WATCH OUT- 1,000 ppm TDS, 100 ppm Na/Cl, 1 ppm B
- Author: Mark Bolda
- Author: Michael D Cahn
Just had a great conversation with Mike Cahn, our Irrigation and Water Resources Advisor in Monterey County regarding the salt issues in the berry fields on the Central Coast.
The Basics of Salinity Measurement: Electrical conductivity (EC) is a measure of the combined effect of all the salts in the soil or irrigation water. Generally in irrigation water an EC of less than 1.5 dS/m is not known to present problems for growing strawberries. Strawberries can often tolerate water of EC above 1.5 if the main salts are calcium and sulfate. Soil EC thresholds for strawberry were based on a saturated paste extract from the soil. A soil paste extract with an EC of 2 or 3 shouldn’t be seen as a big issue for strawberries. Directly measuring soil EC with a probe (see the example in the photo below) will often produce much higher numbers than would be found from a saturated pasted extract because the salts are concentrated in less soil moisture.
There are different types of salt, and some are more harmful than others to the roots of the plant. One way of gauging how great the potential of harm a certain species of salt presents to the plant is how easily it precipitates out of solution – salts which stay in solution easily will tend to get taken up by the plant root when it pulls up the water while those which precipitate out are solid and not capable of being taken up by the plant root.
So, take for example calcium carbonate and calcium sulfate, which are both salts and matter of fact compose most of that white stuff we are seeing on the surface of the soil around here. This white stuff is a precipitate and as a solid won’t be taken up and no longer presents a danger to the plant root. Sodium and chloride on the other hand, stay in solution much more easily and therefore can also be taken up by the plant root. Moreover, since sodium and chloride continue to stay in solution even as water is evaporating away, their concentration rises and they become even more harmful to the plant roots and the plant itself.
Managing Sodium and Chloride: Fortunately, it’s pretty easy to leach away sodium and chloride from around the plant roots. One just needs to add more water to the soil than what is necessary for the plant. Since for example strawberry plants planted in autumn of 2013 are still quite small and the weather has been very cool (meaning low evapotranspiration), Mike estimates probably about a half to 1 inch is all they needed in the last month of December. Any water applied in excess of this amount will leaching away and carrying whatever salt is in solution .
Possible Salt Accumulation from Fertilizers: Since it would seem that harmful levels of sodium and chloride are being leached away by current irrigation practices, Michael and I focused our conversation on the possibility of nitrates from fertilizer – especially the pre-plants- being a major source of the salt damage that we are currently experiencing in our area. Because preplant N is applied in bands near the roots of the transplants and there is little uptake of N at this early stage of growth, nitrate released from the fertilizer may be increasing the salinity near the roots. We calculated that if 90 lbs of N/acre released from 2 bands of fertilizer on 52 inch wide beds, the salinity may increase in the root zone by 3.4 dS/m. During a typical year about 12 inches of rainfall will occur between December and March. During a drought year, it is possible that the irrigation water applied is of sufficient volume to activate the pre-plant fertilizer but not enough to wash it away and so there is a consequent buildup of harmful nitrate (a salt) right around the root ball.
This will be worth looking into in the very near future.