The impact of heated nutrient solution on yield and chemical composition of hydroponically grown 'baby' leaf vegetable

F. Bantis, P. Karnoutsos, M. Karagiovanidis, G. Ntinas, A. Koukounaras
There is a continuous increasing demand for 'baby leaf' vegetables such as lettuce, rocket, spinach, kale, etc. which are offering a wide range of colors, shapes, textures, aromas and tastes. Lettuce and rocket can grow in low cost hydroponic systems such as floating system into a greenhouse with relatively simple air temperature control for optimal growth. The aim of the present study was to examine the responses of 'baby leaf' lettuce and rocket, grown hydroponically in floating system, in a glass greenhouse without climate control, under harsh environmental conditions (winter, early spring) and different water tank heating strategies (heated by the grid and heated by a photovoltaic system). The two heating systems were installed inside two tanks (Hoagland 100%) increasing the temperature at a target of 22°C. Power was provided by solar panels or by connection to public electricity network (control). During the experiment the temperature of the nutrient solution was recorded as well as the energy used while at the end we determined for each 'baby' vegetable the yield, the nitrate content and the antioxidant capacity. According to the results, yield was significantly lower at the photovoltaic tank for both lettuce and rocket during winter period, -23.0 and -31.1% respectively, whereas for early spring period significantly higher yield was recorded at the photovoltaic treatment (+31.2% for lettuce and +19.1% for rocket). Nitrates contents were not affected by the different temperature of nutrient solution as a result of our treatments. On the other hand, in both experimental periods 'baby leaf' of both species had significantly higher antioxidant capacity produced in photovoltaic tank (increase from +1.5 to 14.6%) except early spring period for rocket. Energy utilization was lower at the photovoltaic tank in both experimental periods.
Bantis, F., Karnoutsos, P., Karagiovanidis, M., Ntinas, G. and Koukounaras, A. (2021). The impact of heated nutrient solution on yield and chemical composition of hydroponically grown 'baby' leaf vegetable. Acta Hortic. 1321, 173-178
DOI: 10.17660/ActaHortic.2021.1321.22
lettuce, rocket, floating system, antioxidants, nitrates

Acta Horticulturae