Quantifying direct CO emissions from organic manure fertilizer and maize residual roots using C labeling technique: A field study.

Organic manure compost offers benefits like enhanced crop yield, improved soil health, and increased soil carbon storage. However, its application might elevate direct CO emissions from organic matter decomposition. Beyond manure compost, significant sources of CO emissions in agricultural settings are from residual roots and root exudates of pre-crops, and soil carbon. Quantifying the contribution of these sources to CO 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 C labeling on summer maize to generate C-labeled manure compost and maize root, which is used to differentiate CO emissions from these sources. Our results revealed novel insights into the magnitude and patterns of CO emissions from these sources. The emission pattern of C-CO derived from manure compost, root and root exudates was similar, but the magnitude differed. Specifically, manure compost accounted for 5 % of the total CO 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 CO emissions was derived from the soil and other sources. CO 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 CO 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 CO emissions. This novel research quantifies the direct contribution of individual manure compost to CO emissions, providing valuable data for carbon cycle models and improving understanding of CO contributions from new carbon inputs.