Large variation of fertiliser levels does not improve physiology, nutritional quality and economic return of greenhouse capsicum

Although protected cropping achieves high efficiency to maximise the yield of vegetables, growers tend to overuse fertilisers in greenhouses. This study evaluated the effects of fertigation levels [electrical conductivity (EC) 1.0, 2.5, and 3.5 of nutrient solutions] on the leaf gas exchange, postharvest quality, and nutrition of capsicum to determine the fertigation efficiency for two capsicum cultivars in a high-tech glasshouse. In addition, we extend the agronomic perspective to encompass an economic analysis, assessing the cost-effectiveness of adopting advanced fertigation strategies for greenhouse capsicum. Our results showed that High EC treatment did not improve mophorlogical and post-harvest parameters but decreased the nutritional quality, particularly Ca²⁺ and Mg²⁺, of capsicum leaves and fruits. Similarly, the postharvest quality traits did not improve with high nutrient supply. The highest net present value (NPV) and benefit/cost ratio were recorded in the EC 2.5 scenarios, reaching 529.6 USD·m⁻² and 3.35 in Australia, and 60.4 USD·m⁻² and 2.53 in India, respectively. The modelled commercial-scale capsicum business in Australia was expected to break even after 5.73 to 7.11 years; comparatively, the payback period in India takes slightly longer 5.96–8.31 years. Sensitivity analysis revealed that a 10% yield decrease results in more than 20% of economic loss in Australia and more than 30% in India. Overall, a higher level of fertigation at EC 3.5 did not improve the capsicum fruit’s nutritional properties or economic return. We suggest that the trade-off between fertiliser usage and yield has profound economic implications for the sustainable production of greenhouse capsicum.