Effect of different macronutrient cation ratios on macronutrient and water uptake by melon (Cucumis melo) grown in recirculating nutrient solution

Abstract

The aim of the present study was to determine uptake ratios between macronutrients and water for melon (Cucumis melo L. cv. Dikti) grown in a closed soilless cropping system. The obtained data can be used to establish standard nutrient solution compositions for melon crops grown in closed hydroponic systems under Mediterranean climatic conditions. Nutrient and water uptake by plants in the closed hydroponic system was compensated for by supplying replenishment nutrient solutions (RNS) differing either in the concentrations of K+, Ca2+, and Mg2+ or in their mutual ratio. The RNS, used as control treatment, had an electrical conductivity (EC) of 1.74 dS m−1 and contained 6.5 mM K+, 2.8 mM Ca2+, and 1.0 mM Mg2+ (K+ : Ca2+ : Mg2+ = 0.63 : 0.27 : 0.10). Control RNS was compared with two other RNS, both with a high Ca2+ level (4.2 mM). The K+ and Mg2+ levels in these two RNSs were: (1) not altered (corresponding to a ratio of K+ : Ca2+ : Mg2+ = 0.55 : 0.36 : 0.09; EC = 2.0 dS m−1) or (2) increased to maintain the same K+ : Ca2+ : Mg2+ ratio as in the control RNS (EC = 2.45 dS m−1). Nutrient to water uptake ratios, commonly termed uptake concentrations (UCs), were assessed by two alternative methods, i.e., (1) estimating the ratio between nutrient and water removal from the system or (2) estimating the ratio between the mass of the nutrient that was recovered from plant biomass and the water consumption. Over the two methods, mean UCs for N, P, K, Ca and Mg were 15.4, 1.31, 5.47, 3.78, and 1.02 mmol L−1, respectively, and tissue analysis resulted in a K : Ca : Mg molar ratio of = 0.55 : 0.34 : 0.11 in the whole plant. Moreover, the UCs tended to decrease as the crop aged although, in absolute values, the mass of nutrients absorbed increased following dry‐weight accumulation. Based on the obtained results, adapting the composition of the nutrient solution at least three times during the cropping period of melon is recommended. Further, the results revealed that the damage caused by the increase of the EC when attempting to maintain a target K+ : Ca2+ : Mg2+ ratio in the replenishment NS is higher than the benefits from the optimal cation ratio. Increasing K+ and Mg2+ concentration in addition to that of Ca2+ to maintain a standard K+ : Ca2+ : Mg2+ ratio raises the EC in the root zone (4.62 dS m−1), due to increased accumulation of nutrients, thereby reducing the mean fruit weight and concomitantly the total fruit yield (20% decrease). Leaf gas exchange, chlorophyll parameters and fruit taste quality were not influenced by the differences in macronutrient cation concentrations or ratios in the RNS, whereas phenolics and antioxidant capacity in melon fruit were enhanced by the increased root‐zone EC.

Cascade Cropping System with Horticultural and Ornamental Plants under Greenhouse Conditions

“…Moreover, the reduction in NO3 − , H2PO4 − and K + concentrations in the drainage waters applied for irrigation compared to the nutrient solution could be related to the melon nutrient uptake. Our results were similar with the findings reported by Neocleous and Savvas [26] in the same crop.…”

“…Moreover, the reduction in NO 3 − , H 2 PO 4 − and K + concentrations in the drainage waters applied for irrigation compared to the nutrient solution could be related to the melon nutrient uptake. Our results were similar with the findings reported by Neocleous and Savvas [26] in the same crop. The irrigation with sequential reuse water against standard nutrient solution resulted in an increase of grey water which may be dangerous from an environmental point of view as suggested by Castellanos et al [27], while the irrigation with blended drainage water against standard nutrient solution resulted in an increase of blue water which is a great drawback in areas with water scarcity as mentioned also by Hoekstra et al [28].…”

Comparison of Coconut Coir, Rockwool, and Peat Cultivations for Tomato Production: Nutrient Balance, Plant Growth and Fruit Quality

“…In tomato production, high-EC induced inhibition of Ca absorption is very common in substrate cultivation, which often leads to BER of tomatoes due to Ca deficiency ( Uozumi et al, 2012 ). In this study, as EC in root-zone solution increased gradually during the growing period ( Figure 1 ), BER increased gradually for all substrates from 3rd to 13th trusses ( Table 3 ), indicating the Ca deficiency induced by high EC ( Neocleous and Savvas, 2015 ). This result suggested that inhibition of Ca deficiency was still a challenge for soilless tomato production.…”

“…Despite this, PVC cultivation generally showed the lowest BER ( Table 3 ). This phenomenon could be explained by the fact that (1) peat contained high content of Ca ( Table 1 ) and was able to enhance Ca absorption by tomato crops ( Zhang et al, 2015 ), (2) lower K + /Ca 2+ ratio in root-zone solution under PVC (Supplementary Figure S1 ) reduced K-Ca antagonism in root-zone ( Neocleous and Savvas, 2015 ) and (3) the relatively high buffer ability of peat-vermiculite (PVC) resulted in a relatively stable pH during the growing period ( Figure 1 ) and benefited Ca uptake by tomato crops ( Rippy, 2005 ). Despite the benefits of PVC, no statistical difference in total BER was found between CC and PVC ( Table 3 ).…”

Simulating NaCl accumulation in a closed hydroponic crop of zucchini: Impact on macronutrient uptake, growth, yield, and photosynthesis

“…In the present work, plants in early stages of growth showed increased needs for nutrients compared to the relative water needs, thus, UCs were initially higher than subsequent estimates as the crop aged. This could be explained by the fact that young plants have an increased need for nutrients due to rapid growth, while their water requirements are still small at the same time ( Neocleous and Savvas , ). It is well known that under saline conditions Cl − restricts uptake ( Grattan and Grieve , ).…”