nutrient solution strength salts that conduct electricity when dissolved in a solution , and this conductive property allows growers to accurately measure the strength of a nutrient solution . The higher the conductivity , the higher the concentration of dissolved salts present in a solution . Electrical conductivity ( EC ) or total dissolved solid ( TDS ) meters are the two most commonly used pieces of equipment to measure the concentration of nutrients in a solution . However , TDS meters ( commonly referred to as parts per million [ ppm ] meters ) are really EC meters in disguise . TDS meters measure the EC of a nutrient solution then use a conversion factor of 500 , 640 , or 700 to estimate the ppm of a solution ( depending on the brand of the meter ). Whether you are using an EC or TDS meter , the steps used to measure your nutrient solution are the same . You will first measure the water that you will be mixing your nutrients with to see if your source water contributes to the overall conductivity of the solution . You will then mix your nutrients into the solution and measure the overall conductivity of water and nutrients combined ( if you had any charge in your source water , you will need to subtract that value from the reading if you are trying to achieve a desired EC or ppm ). Depending on your irrigation methods ( hand watering , drip , ebb and flood , etc .) and irrigation frequency , the strength of your solution will need to be adjusted to maintain the optimal level in the root zone for the crop you ’ re growing . While it is very important to know the strength of the nutrient solution applied to your crop , it is equally ( if not more ) important to monitor the amount of soluble salts in your root zone . A simple method used to measure the conductivity of your media is called the pour-thru method . The first step of this method is to irrigate your crop with your nutrient solution until the media is completely saturated . Wait 30 minutes , then place a saucer below the container and pour distilled water over the surface of the media until you collect a sample large enough ( about 50 millilitres ) to be able to submerge the tip of an EC or TDS probe . This reading will indicate whether you need to increase or reduce your nutrient solution concentration , or if you need to flush the root zone with pure water to remove soluble salts .
ENVIRONMENTAL VARIABLES
Several environmental variables will impact how fast water and mineral nutrients are taken up by a plant , including but not limited to light intensity , temperature , and relative humidity . As light intensity (µ mol / m 2 / s ) is increased , the rate of growth also increases and results in a greater demand for nutrients . However , increased light intensity also increases the rate of transpiration , which will cause you to irrigate your crop more frequently . If you are feeding a high rate of fertilizer at each irrigation , this can cause soluble salts to build up in the root zone , resulting in increased osmotic pressure that will make it difficult to for your plants to uptake water and nutrients . Any time you have increased osmotic pressure in the root zone , your growth rate will decrease and yield will be sacrificed . Increasing the air temperature or reducing the relative humidity in your controlled environment will also increase transpiration rates , which will influence your irrigation frequency . The bottom line is this : anytime you are changing environmental variables , it is extremely important to monitor the EC of your root zone to ensure you do not run into issues .
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