Differences in soil carbon sequestration and soil nitrogen among forages used by the dairy industry

Forages cover extensive areas of agricultural land in Australia, but only limited data is available on the potential of these different forages to sequester soil organic carbon (SOC) under best practice management. This study was undertaken on a brown dermosol in the warm temperate climate of Camden, Australia, over three years, to evaluate a range of perennial and annual forages for their impact on SOC and soil nitrogen (N). The C4 perennial forages kikuyu (Pennisetum clandestinum Hochst. ex. Chivov.) and paspalum (Paspalum dilatatum Poir.) increased (P < 0.05) SOC by 7 g/kg from 27 g/kg initially over the three years which was equivalent to an annual increase of approximately 2.6 t C/ha. For the other forage species, the SOC did not change (P > 0.05). The high productivity of legumes led to high mean estimate of N fixation of up to 726 kg N ha/year over the three years. However, as most of the legume shoot production of the forage species was removed there, was a negligible increase in soil N levels. This study has shown that the choice of forage has a large impact on the amount of carbon that can be sequestered into the soil.