Changes in soil carbon in hill-country under contrasting phosphorus fertiliser and sheep stocking rates

Carbon (C) measurements were analysed for soil sampled to two depths (0-75 and 75-150 mm) in 2003 and again in 2014 in three of the farmlets of a long-term phosphorus (P) fertiliser and sheep grazing experiment at the AgResearch Ballantrae Hill Country Research Station. The farmlets received either 125 kg/ ha/year of single superphosphate (SSP) from 1975-1979 and none since (LFNF), or the same amount of SSP applied as for LFNF from 1975-1979 and 125 kg SSP/ha/year since 1980 (LFLF), or 625 kg/ha/year of SSP applied from 1975-1979, and 375 kg SSP/ha/year since 1980 (HFHF). Carbon concentration in soil at both sampling depths was not affected by differences in P fertiliser inputs and sheep stocking rate, but there were significant (P<0.001) slope x farmlet and aspect x farmlet interactions. Data from this long-term study provide science, policy and industry with invaluable insights into the changes in soil C stocks in pastoral hill-country soils.