The effects of bare fallow, pasture, or short-term break crops on soil chemical and
physical properties are being investigated in five rotation experiments in the Sugar
Yield Decline Joint Venture. The experiments are located at Tully, Ingham, Burdekin,
Mackay and Bundaberg. The soil organic carbon at each site is being characterised in
terms of total carbon, charcoal content (inert fraction), and two measures of labile
carbon (particulate organic carbon and permanganate oxidisable carbon). Soil sampling
at the end of the 12,30 or 42 months breaks (duration depending on site) from continual
cane indicated that the break period treatment had effects on soil organic carbon
(0-10 cm). The pasture break caused an increase (significant at P<0.05 at some sites) in
both labile and total organic carbon, while the bare fallow caused a decline (significant
at P<0.05 at some sites) in these values relative to continual cane. Increases in the
content of total and labile organic carbon were associated with increases in cation
exchange capacity at the Tully and Mackay sites, and increases in aggregate stability
and microbial biomass at the Bundaberg site. These results indicate the importance of
break period management for the maintenance of soil fertility (chemical, physical and
biological) in the cane cropping system.