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April 2014

Investigating impacts of Electrical Conductivity in Nutrient Solutions

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In recirculating systems producing leafy crops, one of the main factors in the control of the grower is the nutrient solution electrical conductivity (EC). In many systems, total EC, rather than single elements are controlled due to economics. In most commercial systems using electronic controllers and dosing pumps, concentrated fertilizer solution is added to the nutrient solution any time the solution goes below target EC. So, maintaining consistent EC levels is fairly straightforward, the main question becomes: What is the best EC? The answer to this question is based on two separate factors. The first relates to maintaining needed nutrients in solution. Essentially, the important question is how close to calculated nutrient levels does the solution remain over time. If there are large amounts of ions already in the source water (sodium, sulfate, or calcium for instance), this can cause the nutrient solution to become out of balance more rapidly meaning that ideal ratios of nutrients are not maintained. The second factor involves the movement of water through the plant. At lower EC, it is easier for plants to take up and transpire water. Therefore, under high light and temperature, and low humidity, lower solution EC levels makes it easier for the plant to move water. So, the EC that we use in our systems needs to address these two issues: 1) Maintain adequate levels of plant nutrients, and 2) not stress the plant too much in terms of taking up water needed for transpiration.