Effects of long-term fertiliser inputs on the quantities of organic carbon in a soil profile under irrigated grazed pasture

The long-term fertiliser field trial at Winchmore was used to investigate relationships between pasture production and soil organic carbon (C) storage. In 2009, soil samples to 1 m depth were taken from plots that had been subject to three levels of annual superphosphate fertiliser input for 57 years (nil, 188 kg ha(-1) [188PA] and 376 kg ha(-1) [376PA]). Although annual pasture production was 2.4-2.8 fold higher for the fertiliser treatments compared with nil P, concentrations and amounts of organic C were similar for the various treatments at most soil depths. Furthermore, differences in total quantities of organic C in the soil profile between the nil P (107 t ha(-1)), 188PA (101 t ha(-1)) and 376PA (114 t ha(-1)) treatments were not significant. The absence of any significant accumulation of soil organic C in response to increased production was attributed to accelerated decomposition of organic matter inputs linked to a combination of improved pasture quality and increased earthworm activity.