Effects of Light Calcium Carbonate-Loaded Microbial Inoculants on Nitrogen Transformation and Gaseous Emissions During Chicken Manure Composting

Chicken manure composting is an effective approach for manure recycling, but nitrogen loss and gaseous emissions limit its environmental benefits. This 34-day field-scale experiment investigated the effects of microbial inoculants on nitrogen loss mitigation and gaseous emission reduction during light calcium carbonate (LCC)-amended composting of chicken manure. Three treatments were established: LCC alone, LCC loaded with a commercial microbial inoculant (CMI), and LCC loaded with a specifically designed microbial inoculant (SDMI). Physicochemical properties, NH3, N2O, CO2, and CH4 emissions, and nitrogen-cycling functional genes were monitored. Compared with LCC, CMI and SDMI accelerated compost maturation, with SDMI showing stronger mitigation effects by reducing cumulative NH3 and CH4 emissions by 31.14% and 17.77%, respectively. CMI mainly enhanced AOB-amoA and nirS, whereas SDMI promoted AOA-amoA and nosZI and maintained higher nirS and nosZI abundances during later stages. PLS-SEM analyses revealed that NH3 emissions were mainly regulated by temperature, NH4+-N, EC, and pH, while N2O emissions were jointly affected by physicochemical properties and nitrogen-cycling functional genes. Overall, this study demonstrates that LCC-based microbial inoculation, particularly SDMI, is a promising strategy for regulating nitrogen transformation, reducing nitrogen loss and gaseous emissions, and improving chicken manure resource utilization.