Relationships between denitrification, microbial biomass and indigenous soil properties

The relationships between denitrification, soil microbial biomass and selected soil properties were investigated in 13 soils which varied in physical and chemical properties. It was hypothesized that estimates of biomass C may be directly related to the background (unamended) denitrification rates. Denitrification potential (with C and NO−3 amendments) was also compared to biomass C and the indigenous soil properties. The background and potential denitrification rates were measured in these soils during 75 h of anacrobiosis. Background denitrification was highly correlated with biomass C. organic C content and moisture content at field capacity (−33 kPa). Soil organic C was also highly correlated with microbial biomass C. Nitrate was not limiting for most soils as in all but two soils the residual NO−3 content following incubation exceeded 10mg N kg−1. Hence. NO−3 concentration was not strongly correlated with the background denitrification rate. The denitrification potential was 5 times greater than background denitrification. In our study, C was the factor limiting denitrification. Further, microbial biomass appeared to be a sensitive indicator of both soil C content and background denitrification. There was no significant relationship between any of the other soil chemical and physical properties measured and the denitrification potential.