Olive Pomace Biochar as a Composting Additive: Effects on Greenhouse Gas Emissions, Compost Quality, and Crop Productivity in Arid Soils

The use of biochar as a composting additive has been proposed as a viable option to mitigate greenhouse gas (GHG) emissions while improving compost quality. This study evaluated olive pomace biochar (OPB) as a composting additive, focusing on its effects on GHG emissions during composting, the quality of the resulting compost, and its impact on crop productivity in arid soils. Composting experiments were conducted with and without biochar addition, and emissions of CO₂, CH₄, N₂O and NH₃ were measured during the thermophilic phase of the composting process. Biochar reduced cumulative CH₄, N₂O and NH₃ emissions by 87.4, 57.3 and 59.2%, respectively compared to the control. The addition of biochar also increased the content of organic carbon by 87% and nutrients (N by 18%, P by 34% and K by 26%. The fertilizing value of the composts was evaluated in a six-week greenhouse experiment using maize (Zea mays L.) grown in an arid soil. Biochar-amended compost increased plant biomass by 53% compared to conventional compost, demonstrating positive effects on early crop growth. The plant content of N, P and K increased by 49, 66 and 51% in soil treated with biochar-amended compost relative to the control. A field experiment evaluating crop productivity and soil properties was also carried out, and its data analysis is still in progress and complete results will be presented when completed. Overall, the findings highlight the potential of OPB-enhanced composting as a possible strategy to reduce GHG emissions, improve compost quality and crop performance in arid agroecosystems.