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Water Conductivity and Soil Salinity
- Why Are Tests So Important
- What is Conductivity
- Conductivity and Water Quality
- Conductivity and Soil Salinity
- Creating Soil Samples
- Conductivity and Fertilizer Concentration
- Alkalinity
- Conclusion
Why Are Tests So Important
Modern growing practices include scientific evaluations of soil, water, fertilizers, diseases, etc. While some tests are best performed by a laboratory, others can be easily conducted on location, saving time and money. Three tests in particular, CONDUCTIVITY, pH, and ALKALINITY can reveal valuable information about water quality, soil salinity and fertilizer concentration.What is Conductivity?
Conductivity is the measurement of a solution's ability to conduct an electrical current. For horticultural applications, the unit of measure is often expressed as milliohms. Absolutely pure water is actually a poor electrical conductor. It is the substances (or salts) dissolved in the water which determine how conductive the solution will be. Therefore, conductivity can be an excellent indicator of:- Water quality
- Soil salinity
- Fertilizer concentration
Conductivity and Water Quality
The quality of irrigation water is one of the most critical factors influencing your growing operation. It is important to have a complete water analysis performed on a regular basis. Environmental conditions such as drought, changing seasons, heavy rainfall, etc. can cause the concentration of dissolved salts in your water to vary significantly. These dissolved salts (i.e. calcium, sodium, etc.) can directly affect your plants health and over time, render even the best soil useless.You can monitor your overall water quality by testing its electrical conductivity. The higher the conductivity, the more salts are dissolved in your water. By comparing your conductivity readings on a regular basis you can tell if any dramatic changes have occurred. Nutrient deficiencies are possible when water is too pure (low conductivity) or if the relative concentration of some nutrients are unbalanced (i.e.. Calcium/Magnesium).
Conductivity and Soil Salinity
Salts from irrigation water and fertilizers tend to accumulate in your soil or growing media. High soil salinity disrupts the normal osmotic balance in plant roots. In severe cases a plant will become dehydrated even when the soil is wet. Symptoms of high soil salinity include:- leaf chlorosis and necrosis
- leaf drop
- root death
- nutrient deficiency symptoms
- wilting
Creating Soil Samples
Samples of soil should be representative of different depths and locations. An easy-to-perform extract method is to take two parts distilled water to one part soil. Note some organic media such as peat most may need a five part distilled water to one part soil. Only a heaping tablespoon of soil is required. Agitate the container vigorously. Let settle for 45-60 minutes and decant the water in a separate cup. If you are comparing your results with the one from a soil lab make sure you standardize your sampling, extract and testing methods with the lab. Most labs use a much thicker slurry and hence usually produce much higher soil conductivity concentrations.
Conductivity and Fertilizer Concentration
You know how important fertilizer is to your plants, but do you know how accurate your fertilizer dosage is? Relying on traditional proportional methods is risky to plants and can waste expensive fertilizer. Improperly mixed fertilizer or a malfunctioning injector can lead to less than optimal results or even a disastrous loss of crops. Many fertilizer companies now recommend using a simple conductivity test to verify correct fertilizer concentrations. Many growers check their fertilizer injectors on a weekly basis.Fertilizer companies and suppliers often can provide a chart relating conductivity to parts per million concentrations of their various fertilizers.
To test the conductivity of fertilizer solutions:
- Test and record the conductivity of the water to be mixed with the fertilizer.
- Test the conductivity of the fertilizer and the water mixture.
- Subtract the water conductivity determined in step #1 above.
- The resulting figure is an accurate indication of how much fertilizer is present(a higher conductivity means more fertilizer).
Alkalinity
It is important to note that testing the pH or Conductivity of the water only reveals part of the story. Testing water alkalinity (bicarbonates and carbonates) is much more important than generally recognized. Alkalinity dictates how much influence the water's pH will have on the soil and nutrient availability. In addition, alkalinity has a very great effect on the ease and difficulty of reducing the pH of water.Conclusion
Growing crops efficiently and for the greatest profits requires more than just hard work. With the instruments available to growers today much of the guesswork about: to irrigate or not to irrigate, to fertilize or not to fertilize, has been solved. No longer does the grower have to wait days to get the vital information that he or she needs today.Using conductivity meters, pH meters, alkalinity tests and more reveal to the grower the relationship of the soil and water to the plants.
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