MANAGING A SIMPLE SYSTEM TO RECYCLE NUTRIENT SOLUTION TO GREENHOUSE TOMATO GROWN IN ROCKWOOL

Using recycled nutrient solution to water plants is the preferred legislative solution to prevent groundwater pollution from intensive agricultural production. Several potential problems may arise from recycled nutrient solutions to produce vegetable crops. Accumulation or deficiency of elements in nutrient solutions could 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 periodically recycled to a greenhouse tomato crop (Solanum lycopersicon L.), in comparison to solutions that were used to water plants only once. Crops were grown in spring and summer in a greenhouse using rockwool as the root medium. The transition from vegetative to fruit growth, and from cool to warm weather, resulted in a decreased demand for nitrate, and other nutrients, and an increase in electric conductivity of water drained from the root zone. These changes were greater for recycle than discharge systems, and the recycle treatment took longer to return to an optimal composition. There were no consistent effects on yield, and little difference in composition of fruit or vegetative tissue, despite the large but temporary variation in composition of the nutrient solution due to recycling.