The 2009 ASHS Annual Conference

Recirculation of nutrient solution, or reuse of solution after it has once been used to water plants, is the preferred legislative solution to prevent ground water pollution from intensive agricultural production.  There are several potential problems that may arise due to recirculation of nutrient solutions used to produce vegetable crops.  Changes in composition of nutrient solutions could ultimately have deleterious effects on plant growth, product quality, and the dietary value of vegetables.  We examined the composition of a nutrient solution as it was continuously recirculated to a greenhouse tomato crop, in comparison to solutions that were used to water plants only once. Crops were grown in spring and summer in two years in a heated greenhouse using rock wool as the root medium. The difference in composition of recycled compared to discharged solution developed over more than one month of recycling. Typically, the transition from vegetative to fruit growth, which coincides with the beginning of the warm season, resulted in over-supply of nitrate, potassium and other nutrients. It took a longer time to return the solution to an optimal composition with recycled compared to discharged solution. There was little effect on composition of plants, despite the large but temporary differences in composition of nutrient solution. Yield components of cultivars tended to differ in response to recycling.