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

BACKGROUND The use of water containing calcium bicarbonate (Ca(HCO 3 ) 2 ) at excessively high concentrations in closed hydroponic crops can cause calcium ion (Ca 2+ ) accumulation in the recycled nutrient solution (NS) and concomitantly negatively affect yield and product quality. The aim of the study was to determine maximum Ca 2+ concentrations that do not harm the crop and to simulate the pattern of Ca 2+ accumulation when the Ca 2+ concentration in the irrigation water, and concomitantly in the replenishment nutrient solution (RNS), is excessive. In the current study, irrigation water containing 1.5, 3.0, 4.5 and 6.0 mmol L −1 Ca 2+ was used to prepare the RNS supplied to pepper cultivated in a closed hydroponic system. RESULTS At 1.5 mmol L −1 Ca 2+ , no Ca 2+ accumulation was observed in the recirculating NS. However, at 3.0, 4.5 and 6.0 mmol L −1 in the irrigation water, the Ca 2+ 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 Ca 2+ in the recirculating NS affected both tissue nutrient concentrations and uptake concentrations of Ca 2+ , sulphate ion (SO 4 2− ) and magnesium ion (Mg 2+ ), but this was not the case for nitrogen (N) or potassium ion (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 Ca 2+ levels. CONCLUSION In soilless pepper crops with zero discharge of fertigation effluents, the Ca 2+ concentration in the irrigation water and the RNS should be lower than 3.0 mmol L −1 to avoid yield restrictions due to salinity. © 2021 Society of Chemical Industry