Nutrient uptake concentrations in a cucumber crop grown in a closed hydroponic system under Mediterranean climatic conditions as influenced by irrigation schedule

Preliminary observations have indicated that the nutrient-to-water uptake ratios in crops grown hydroponically in Mediterranean greenhouses may be substantially different than in north-European greenhouses, due to differences in climatic conditions. Furthermore, irrigation schedule may also have an impact on nutrient and water uptake. In the present study, the nutrient to water uptake ratios, commonly termed uptake concentrations (UC), were estimated in a spring crop of cucumber grown in a closed hydroponic system with zero discharge of drainage solution using pumice as growing medium. Three different irrigation schedules aimed at obtaining three target drainage percentages (DP), specifically 15%, 30%, or 45% of the total nutrient solution supply, were compared. Mean UC of macro- and micro-nutrients were determined following two alternative methods. According to the first method, apparent UC were estimated for three successive time intervals by measuring the nutrient and water removal from the recirculating nutrient solution. According to the second method, mean UC for the entire growing season were estimated on the basis of total nutrient recovery from the whole plant biomass and total water consumption. The UC of K, Ca, Mg and Fe, when calculated on the basis of nutrient and water removal from the nutrient solution, were significantly higher than those estimated by measuring the amounts of nutrients in the total plant biomass and the water consumption. Possible explanations for these differences, which were more marked for Mg and Fe, are discussed. When the calculations were based on nutrient and water removal from the nutrient solution, the UC was significantly lower for K, but higher for Mg, than those found under north-European (Dutch) climatic conditions. With respect to Ca, the UC obtained before the start of harvesting were higher than under north-European climatic conditions, but tended to decrease to values similar with the latter after the start of harvesting. The irrigation treatments did not have a consistent effect on the UC of K, Ca, Mg, and Fe, although a slight decrease was observed in some cases, as the DP increased.