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