Hydroponic lettuce is usually grown by continuously recycling the nutrient solution during production. As nutrients are absorbed by plant roots, stock solution is added to the recycled solution to maintain the electrical conductivity (EC) at a target level. Because plants absorb nutrients from the solution at different rates, the recycled solutions accumulates elements which are slowly absorbed by the roots overtime. Therefore, periodic draining of the recycled solution is recommended to avoid negative effects on plant growth and quality. The research addresses two questions: (i) what is the effect of accumulated fertilizer salts on the plant growth of lettuce and (ii) is there a benefit of adjusting EC of the nutrient solution based on plant growth rate and water use as opposed to maintaining a target EC, and (iii) what is the best way to adjust nutrient solution concentration without impacting plant growth and with minimal environmental impact.
