Effects of Microbial Biomass on the Priming Effects of Ryegrass on Native SOM Mineralization.

The objective was to investigate how microbial biomass and N availability affect the priming effect of ryegrass on native SOM mineralization. Soil samples were collected from Russell Ranch Sustainable Agricultural Facility of University of California, Davis. Soils were from a conventional 2-yr rotation cropping system and an adjacent grassland, with contrasting management in the same soil. A portion of the soils was amended with a minimum amount of glucose together with ammonium sulfate to boost the microbial biomass and no changes in microbial community. All soils with and without glucose pre-amendment were incubated with deionized water, 13C-ryegrass residue, or hot water extracted 13C-ryegrass combined with or without N at 22°C for 42 days. Finally, we determined the fraction of CO2 production derived from ryegrass and native SOM, followed by priming effect of ryegrass addition on CO2 production from native SOM.