Kelpak treated lettuce, cv. 'Hawking', outdoor grown in a DFT (Deep Flow technique) system with reduced nitrogen occasionally showed significant differences in comparison to untreated control grown in the same conditions: at some assessments/stress situations Chlorophyll Red and the NDRE were significantly higher. But also, at some assessments/stress situations significantly more stress was measured and and less chlorophyll (NDRE). Analysis of the harvested crop showed - depending on the stress situation - significantly higher concentrations nitrogen, phosphorus and copper per kg dry matter. At other assessments/stress situations the concentrations iron, zinc and copper were lower than in the untreated control.