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ukcheesehead
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Leachate (run off) measurement for tap or ground water (non R.O water).
This technique requires you to measure the conductivity of the water draining from the plants after irrigation. This is perhaps the most practical method for indoor growers.
First you measure the conductivity of the fresh nutrient solution. After irrigating, measure the conductivity of the leachate (run off). This is the water draining from the bottom of the pot. This should measure about 3CF; 0.3E.C. or about 240ppm higher than the original nutrient solution. If the drainage water conductivity is higher than these guidelines, then you are not irrigating enough and you should increase frequency and volume of irrigation. If the conductivity is lower and you are not using de-ionised water and the plants are more than about three weeks old, then you are probably giving them too much water. As cocopeat drains well, this is not as big a problem as under watering. However, it is possible to over water and thus deprive plant’s roots of essential oxygen. With all run to waste systems, you would usually need to have between 20% to 40% running out of the medium depending on the quality of the water supply and the stage of growth of your plants. A safe minimum figure is about 30% run to waste but it may be less when the plants are small and much more with larger plants and water that is a bit saline. Generally, in the first couple of weeks of growth you will get a lot of the water running through the pot as at this stage, uptake is low but a reasonable amount of water is required to keep the medium moist. In this case there is often no change in the conductivity between what goes in and what comes out. That is, if you water with one litre of water, you will get most of that one litre of water draining out. Try to water young plants in such a way that you get just a little bit of drainage.
With larger plants the idea behind giving an amount of water that will produce the 20% to 40% run off is to wash out the unused nutrient salts and the accumulated sodium chloride (salt) that is introduced into the medium along with the bore or tap water. If you are in doubt then 40% run to waste would be a happy medium. It is a good idea to give one watering with plain water once week to help flush out salts. On no account should you do this for more than one day at a time. If you are using very hard water you should flush the medium with a mild nutrient solution rather than plain water.
This technique requires you to measure the conductivity of the water draining from the plants after irrigation. This is perhaps the most practical method for indoor growers.
First you measure the conductivity of the fresh nutrient solution. After irrigating, measure the conductivity of the leachate (run off). This is the water draining from the bottom of the pot. This should measure about 3CF; 0.3E.C. or about 240ppm higher than the original nutrient solution. If the drainage water conductivity is higher than these guidelines, then you are not irrigating enough and you should increase frequency and volume of irrigation. If the conductivity is lower and you are not using de-ionised water and the plants are more than about three weeks old, then you are probably giving them too much water. As cocopeat drains well, this is not as big a problem as under watering. However, it is possible to over water and thus deprive plant’s roots of essential oxygen. With all run to waste systems, you would usually need to have between 20% to 40% running out of the medium depending on the quality of the water supply and the stage of growth of your plants. A safe minimum figure is about 30% run to waste but it may be less when the plants are small and much more with larger plants and water that is a bit saline. Generally, in the first couple of weeks of growth you will get a lot of the water running through the pot as at this stage, uptake is low but a reasonable amount of water is required to keep the medium moist. In this case there is often no change in the conductivity between what goes in and what comes out. That is, if you water with one litre of water, you will get most of that one litre of water draining out. Try to water young plants in such a way that you get just a little bit of drainage.
With larger plants the idea behind giving an amount of water that will produce the 20% to 40% run off is to wash out the unused nutrient salts and the accumulated sodium chloride (salt) that is introduced into the medium along with the bore or tap water. If you are in doubt then 40% run to waste would be a happy medium. It is a good idea to give one watering with plain water once week to help flush out salts. On no account should you do this for more than one day at a time. If you are using very hard water you should flush the medium with a mild nutrient solution rather than plain water.
