Effects of C/N ratio and pH value on the decomposition of a mixture of Populus alba×P. berolinensis-Hosta plantaginea fallen leaves and turf grass clippings

Objective  Using Populus alba×P. berolinensis-Hosta plantaginea fallen leaves and turf grass clippings as basic materials, to screen the optimum decompositon condition of mixed materials by adjusting C/N ratio and pH value.

Method  The mixed materials of P. alba×P. berolinensis-H. plantaginea fallen leaves and turf grass clippings were cultured in thermostatic room for 60 days to conduct aerobic decomposition. Different C/N ratios (10, 15, 20) and pH values (4, 7, 10) were setted to explore their effects on contents of water soluble organic carbon (WSOC), humic-extracted acid C(HEC), humic acid C(HAC), fulvic acid C(FAC) and humin C(HuC) during the decomposition process.

Result  HEC and HAC extracted from the mixed materials were both accumulated at the end of culture while C/N ratio was 10 or 15, and C/N ratio of 20 was more beneficial to the microbial mineralization and turnover of WSOC, HEC and HuC. When C/N ratio was 15 or 20, the humic quality of mixed materials was enhanced after 60 days of culture. The transformation of FAC to HAC was partly restrained if C/N ratio was set to 10 by applying more nitrogen into the mixed materials. The C/N ratio of 20 was more beneficial to the simplification of humic acid (HA) molecular structure, followed by C/N ratio of 10. C/N ratio of 15 was more favorable to the stabilization of HA molecular structure. The microbial mineralization of HuC could be promoted when pH value of mixed materials was 7, and the contents of HEC and HAC were increased by 30.0% and 69.0% respectively in the decomposition process. When pH value of mixed materials was adjusted to 10, HAC/FAC ratio was mostly promoted and increased by 78.3%, while pH value of 4 or 7 had relatively smaller effect on HAC/FAC ratio promotion.

Conclusion  The combination of C/N ratio of 15 and pH value of 7 mostly promotes the decomposition of mixed materials composed with P. alba×P. berolinensis-H. plantaginea fallen leaves and turf grass clippings.