Environmental trade-offs of pig manure digestate reuse in solid and liquid soilless cherry tomato cultivation

Biowaste valorization, particularly of livestock manure, supports nutrient recovery and net-zero commitment in circular agriculture. However, the environmental performance of biowaste reuse under real cultivation conditions remains insufficiently quantified, especially in soilless systems where the interaction between nutrient precision, system design, and biowaste-derived inputs has not been adequately resolved. To address this gap, this study developed a field-to-life cycle assessment (LCA) workflow for pilot-scale soilless cherry tomato cultivation, integrating experimental data with LCA to directly compare conventional fertilizers with pig manure digestate (aerobic pretreatment, 10% (v/v) substitution) in solid- and liquid-based systems. Using 1 kg of marketable cherry tomatoes as the functional unit and a cradle-to-gate system boundary from seeding to harvesting, results showed that digestate improved the environmental performance of the solid-based system, reducing the selected midpoint impact categories by 9-21% through higher yields (25.3%) and lower energy demands. In contrast, the same digestate input was associated with increased the selected midpoint impact categories by 29-43% in the liquid-based system, driven by lower yields (22.6%) and higher electricity use for circulation. The liquid-based systems also showed uncertainty ranges 2-9 times wider than those of solid systems, reflecting greater sensitivity to yield variability and electricity consumption and indicating greater uncertainty in estimated environmental performance under the evaluated conditions. Overall, these findings demonstrate that the environmental value of biowaste valorization depends on system configuration, crop yield response, and nutrient management, and should be assessed as a system-specific sustainability intervention rather than solely as fertilizer substitution.