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(HCO3)(2)) at excessively high concentrations in closed hydroponic crops can cause calcium ion (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 solution (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+, sulphate ion (SO42-) and magnesium ion (Mg2+), 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 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. (c) 2021 Society of Chemical Industry