Different organic composts application in dryland Mollisol:Residual effect and soil CO₂ emission

Organic compost application plays an important role in improving the fertility of Mollisol. However, the effects of different organic composts on carbon sequestration varies greatly and its internal mechanism are unclear. We conducted a field experiment to explore the residual proportion of different organic composts and their effects on carbon emissions in dryland Mollisol in Northeast China. There were a total of seven treatments, including chemical fertilizer control (SNF), organic composts from cattle excreta (CRH), sheep excreta (SHP), chicken excreta (CKN), residue after corn starch production (BCS), residue with crop straws (HRS) and mushroom residue (WMC). We monitored annual soil CO₂ flux by static chamber method, as well as the changes of environmental factors and soil dissolved carbon and nitrogen. The regulatory mechanism of organic component characteristics on carbon residual porprotion of organic composts were examined by neural network analysis. The results showed that compared with the SNF treatment, soil dissolved organic carbon (DOC) and extractable organic nitrogen increased by 26.3%-103.5% and 21.4%-150.0%, respectively. The aromaticity of soil DOC was significantly reduced. Heterotrophic respiration flux was mainly affected by soil temperature and DOC content, while its temperature sensitivity was significantly reduced in the CKN treatment. Annual accumulation of heterotrophic respiration increased from 203 g·C·m^-2 of the control to 234-334 g·C·m^-2 under treatments with organic composts applications, with the CKN and HRS treatments showing the strongest impact. The annual carbon residual proportion of different organic composts in Mollisol was in an order of CRH (91.2%)> WMC (82.9%)> BCS (82.6%)> SHP (78.1%)> CKN (70.2%)> HRS (69.3%). Hemicellulose content and C/N of organic composts were the key factors, which explained 58.8% and 32.9% of the total variations of carbon residual proportion. Organic compost from cattle excreta had higher residual proportion due to lower C/N, hemicellulose content and soluble polyphenol content, and thus did not significantly affect Mollisol heterotrophic respiration. Therefore, the application of organic compost from cattle excreta was more efficient to improve organic carbon in dryland Mollisol.