Solar drying for low-emission agri-food systems: Linking post-harvest management with carbon–nitrogen dynamics

Global agricultural systems face increasing pressure from climate change, resource constraints, and the need to ensure food and nutritional security. Post-harvest losses represent a significant yet often overlooked source of greenhouse gas (GHG) emissions, as the decomposition of unmanaged biomass releases CO₂, CH₄, and N₂O, intensifying carbon (C) and nitrogen (N) fluxes. Solar-assisted drying offers a low-emission and nutrient-conserving alternative to conventional fossil fuel-based drying technologies. By utilizing renewable solar energy, greenhouse and hybrid drying systems can achieve lifecycle CO₂ emission reductions of approximately 40–70%, while simultaneously reducing drying times by 40–70% relative to traditional methods. Rapid moisture removal suppresses microbial activity, thereby limiting methane generation and reducing nitrogen losses through volatilization and leaching. Available evidence indicates avoided methane emissions of approximately 0.2–0.5 t CO₂-eq per ton of perishable waste, although reported values vary with biomass characteristics, storage conditions, system boundaries, and methodological assumptions. Controlled solar drying commonly operates within temperature ranges of approximately 45–60°C, although optimal conditions vary according to product characteristics, moisture content, and quality requirements. Such controlled drying can improve the retention of proteins, vitamins, antioxidants, and other quality attributes compared with open-sun drying. Recent technological developments, including hybrid energy integration, thermal energy storage, Internet-of-Things (IoT)-based monitoring, and intelligent process control, have further enhanced system efficiency, reliability, and climate resilience. This review examines solar drying within a Carbon–Nitrogen–Food (CNF) nexus framework that links post-harvest management with emission mitigation, nutrient conservation, and food-system sustainability. By explicitly connecting moisture control with carbon and nitrogen dynamics, the study provides a systems-level perspective on the role of solar drying in supporting low-emission, resource-efficient, and climate-resilient agri-food systems.