Quantifying direct CO₂ emissions from organic manure fertilizer and maize residual roots using ¹³C labeling...

Organic manure compost offers benefits like enhanced crop yield, improved soil health, and increased soil carbon storage. However, its application might elevate direct CO₂ emissions from organic matter decomposition. Beyond manure compost, significant sources of CO₂ emissions in agricultural settings are from residual roots and root exudates of pre-crops, and soil carbon. Quantifying the contribution of these sources to CO₂ emissions is crucial for maximizing carbon reduction in crop-livestock systems, yet field studies have not assessed this contribution. Our study at the Yucheng field station in Shandong Province, China employed ¹³C labeling on summer maize to generate ¹³C-labeled manure compost and maize root, which is used to differentiate CO₂ emissions from these sources. Our results revealed novel insights into the magnitude and patterns of CO₂ emissions from these sources. The emission pattern of ¹³C-CO₂ derived from manure compost, root and root exudates was similar, but the magnitude differed. Specifically, manure compost accounted for 5 % of the total CO₂ emissions, while residual roots and root exudates contributed 2 % and 57 %, respectively, suggesting a higher labile carbon content in root exudates. The remaining 36 % of CO₂ emissions was derived from the soil and other sources. CO₂ emission factors were 6 % for manure compost, 12 % for roots, and 2 % for root exudates. By quantifying the direct emissions from manure compost, residual roots, root exudates, and soil, our study highlights the dominant role of managing root exudates in overall CO₂ emissions. These findings can guide targeted carbon reduction strategies, emphasizing the importance of managing root exudates and understanding the relative innocuousness of manure compost applications in the context of CO₂ emissions. This novel research quantifies the direct contribution of individual manure compost to CO₂ emissions, providing valuable data for carbon cycle models and improving understanding of CO₂ contributions from new carbon inputs.