Modelling Ca2+ accumulation in soilless zucchini crops: Physiological and agronomical responses.

Soilless zucchini ( Cucurbita pepo L.) crops were grown in two distinct cropping periods (spring-summer; SS and autumn-winter; AW) using irrigation water with different Ca 2+ concentrations (1.5, 3, 4.5 and 6 mM). The objectives of this study were to: (i) mathematically correlate the accumulation of Ca 2+ in the root environment with the respective Ca 2+ /water uptake ratio (namely uptake concentration; UC), and (ii) determine the UC of macronutrients (i.e., N, P, K, Ca and Mg) under these conditions. Equations of the literature, initially developed to predict NaCl accumulation in a closed hydroponic system, were further extended to fit experimental results. The evolution of Ca 2+ accumulation in the drainage exhibited a sigmoid pattern with time and the relationship between the concentration of Ca 2+ in the root zone and the corresponding uptake ratio Ca 2+ /water was better described by curvilinear functions. Validation of the model showed a very good agreement between simulated and measured values. Increasing Ca 2+ levels affected both tissue concentrations and UC of Ca and N, but this was not the case for P, K, and Mg. Photosynthesis, growth, yield and plant water uptake were restricted (avg. 15% decrease) at high external Ca 2+ levels, due to high total salt concentration (EC) in the recycled solution (4.2–5.5 dS m −1 ). Fruit quality attributes, however, remained unaffected by treatments with the exception of fruit nitrate content. The empirical model parameterized and tested in this work may serve as a tool to predict Ca 2+ ion concentrations in the root environment of zucchini crops as relationships of the water absorbed by the crop. Finally, the results showed that in soilless zucchini crops with zero discharge of fertigation effluents, there is no compelling reason not to use irrigation water resources with Ca 2+ concentration up to 3 mM. [ABSTRACT FROM AUTHOR]