Comparing the Nutritional Needs of Two Solanaceae and One Cucurbitaceae Species Grown Hydroponically under the Same Cropping Conditions

Abstract

Switching over to closed-loop soilless culture systems, thus preventing pollution of water resources by nitrates and saving water and fertilizers, requires accurate estimations of the mean nutrient-to-water uptake ratios. To contribute to this objective, three fruit vegetable species (tomato, eggplant, cucumber) were grown hydroponically in a floating system under identical cropping conditions to quantify species differences in nutrient uptake. The composition of the nutrient solution used to feed the crops was identical for all species. The total water consumption and the concentrations of most nutrients (K, Ca, Mg, N, P, Fe, Mn, Zn, Cu, B) in the nutrient solution and the plant tissues were measured at crop establishment and at two different crop developmental stages. The obtained data were used to determine the uptake concentrations (UCs) using two mass balance models, one based on nutrient removal from the nutrient solution and a second based on nutrient recovery in the plant tissues. The experiment was conducted in the spring–summer season. The results revealed that the nutrient uptake concentrations were substantially different between species for all nutrients except for N, while there were also significant interactions between the two methods used for their estimation of some nutrients. Thus, the UCs of N, P, Ca, and some micronutrients were significantly higher when its estimation was based on the removal of nutrients from the nutrient solution compared to recovery from plant tissues, presumably because with the first method, losses due to denitrification or precipitation could not be separated from those of plant uptake. The comparison of the three greenhouse vegetables revealed a similar UC for nitrogen, while cucumber generally showed significantly lower UCs for P and for the micronutrients Fe, Zn, and Cu at both cropping stages compared to the two Solanaceae species. The obtained results can be used to precisely adjust the nutrient supply in closed-loop soilless cultivations to the plant uptake thus avoiding both depletion and accumulation of nutrients in the root environment.

Comparison of Methods to Determine Nutrient Uptake of Tomato Grown in Free-Draining Perlite Substrate—Key Information for Optimal Fertigation Management

“…The higher values of nutrient uptake obtained by the balance method compared to the dry matter method in the present work, and by Voogt [35] and Heisen et al [36], are consistent with several recent studies that determined nutrient uptake concentration by the same two methods [40][41][42][43]. Uptake concentration is the uptake of a given nutrient divided by water uptake over the same time period [26][27][28][29].…”

“…The results reported in this work demonstrate the necessity to differentiate between nutrient uptake of a crop and nutrient consumption of a growing system, as was commented by Neocleous and Savvas [41] and by Xaxiri et al [40]. The dry matter method estimates nutrient uptake of the crop.…”

“…Uptake concentration is the uptake of a given nutrient divided by water uptake over the same time period [26][27][28][29]. In tomato, cucumber, and eggplant, the uptake concentrations of N, P, and Ca were clearly higher when using the balance method to determine crop nutrient uptake [40]. In another study with tomato, the uptake concentrations of N, K, and Ca were higher when determined with the balance method than with the dry matter method [42].…”

“…During the vegetative stage of a tomato crop, uptake concentrations of P, K, and Mg were higher when using the balance method to determine crop nutrient uptake [41]. Xaxiri et al [40] suggested that precipitation and gaseous N losses were responsible for the higher uptake concentration values determined using the mass balance method compared to the dry matter method.…”

“…The present study, together with the available scientific literature, suggests that, in soilless cropping, values of nutrient uptake determined by the mass balance method generally exceed those determined by the dry matter method. The processes responsible are not clearly understood, but processes such as precipitation [40,41], direct retention on substrate, and gaseous losses of N and S [34] are likely to be involved. In the present study, there were a small number of instances (e.g., K in the Autumn and Long Cycle crops, Ca in the Autumn crop) where the values for the residual difference, after considering perlite and root retention, were high (Table 4).…”