Responses of sweet pepper (Capsicum annum L.) cultivated in a closed hydroponic system to variable calcium concentrations in the nutrient solution

Abstract

BACKGROUND The use of water containing Ca(HCO₃)₂ at excessively high concentrations in closed hydroponic crops can cause Ca²⁺ accumulation in the recycled nutrient solution (NS) and concomitantly negatively affect yield and product quality. The aim of the study was to determine maximum Ca²⁺ concentrations that do not harm the crop and to simulate the pattern of Ca²⁺ accumulation when the Ca²⁺ concentration in the irrigation water, and concomitantly in the replenishment nutrient solutions (RNS), is excessive. In the current study, irrigation water containing 1.5, 3.0, 4.5 and 6.0 mmol L^‐1 Ca²⁺ was used to prepare the RNS supplied to pepper cultivated in a closed hydroponic system. RESULTS At 1.5 mmol L^‐1 Ca²⁺, no Ca²⁺ accumulation was observed in the recirculating NS. However, at 3.0, 4.5 and 6.0 mmol L^‐1 in the irrigation water, the Ca²⁺ concentration in the recirculating NS, increased by the latter cropping stages to 17, 28 and 37 mmol L^‐1, corresponding to 6.4, 9.0 and 10.8 dS m^‐1. The accumulation of Ca²⁺ in the recirculating NS affected both tissue nutrient concentrations and uptake concentrations of Ca²⁺, SO₄^2‐ and Mg²⁺, but this was not the case for N⁺ and K⁺. Growth, yield and plant water uptake were restricted at moderate (3.0 and 4.5 mmol L^‐1) and high (6.0 mmol L^‐1) external Ca²⁺ levels. CONCLUSION In soilless pepper crops with zero discharge of fertigation effluents, the Ca²⁺ concentration in the irrigation water and the RNS should be lower than 3.0 mmol L^‐1 to avoid yield restrictions due to salinity.