Carbon dynamics in a 60 year fallowed loamy-sand soil compared to that in a 60 year permanent arable or permanent grassland UK soil

Abstract

To determine if the soil microbial biomass in a 60 year fallow soil of the Highfield Ley-Arable Experiment at Rothamsted Research, UK, had maintained its ability to mineralise soil organic matter and added substrates compared to biomasses in a grassland and arable soil of the same experiment. Three soils of the same type: a 60 y permanent fallow, arable and grassland, were incubated (25°C, 40% WHC) with and without 1. a labile substrate (yeast extract, C/N ratio 3.6) or 2. more resistant ryegrass, (< 2 mm, C/N ratio 14.6). Measurements included biomass C, ATP, PLFAs and substrate C mineralization. Mean biomass C and ATP concentrations were:grassland.arable.fallow, as expected. However, substrate C mineralization was less in the grassland than fallow soil, opposite to that expected. Microbial biosynthesis efficiency (measured as biomass C and ATP) was similar in all soils. However, microbial community structure differed significantly between soils and treatments. The extent of mineralization of both substrates were unrelated to initial microbial community structure, size or soil management. Thus, the biomass in the fallow soil maintained full metabolic capacity (assessed by CO2-C evolution) compared to permanent arable or grassland soils.