Carbon-Rich Waste-Derived Fertilizers: Impacts on Soil Carbon Dynamics and Plant Growth

This study presents a comprehensive approach to producing high-carbon fertilizers from carbon-rich waste streams, including anaerobic digestate, sewage sludge, chicken manure, and oilcake. The proposed formulations were developed using chemical hydrolysis, immersion biosorption, and a novel spraying method to enrich organic-mineral fertilizers with essential micronutrients tailored for cucumber cultivation. Analytical results confirmed significant improvements in soil fertility, plant biomass, and microbial activity compared to both untreated waste and reference fertilizers. Formulations F1 and F2 enhanced nutrient availability by up to 30%, while F3 and F4 enabled safe nutrient recycling from sewage sludge and manure. Oilcake-based fertilizers functionalized through biosorption exhibited precise micronutrient delivery and high binding efficiency, with the spraying method outperforming immersion. All fertilizers complied with EU Regulation 2019/1009 in terms of nutrient content and toxic element thresholds, and microbial safety was also confirmed. The study demonstrates the compatibility of selected feedstocks with Component Material Categories (CMCs) under EU legislation, supporting the use of recycled inputs in sustainable fertilizer development. The integration of waste-based inputs addresses environmental, economic, and regulatory challenges in agriculture, contributing to circular economy goals, reduced greenhouse gas emissions, and improved resource efficiency. The findings align with the EU’s Common Agricultural Policy and highlight the potential for large-scale deployment of standardized, cost-effective fertilizers derived from organic waste.