Studies of 'available' and isotopically exchangeable sulphur in some North Queensland soils

Using 35S-sulphate, the specific activity of various sulphur fractions in some diverse North Queensland soils has been followed for up to 185 days in a glasshouse experiment. The sulphur extracted with 0.01 M calcium phosphate was from the same pool as that used by the test plants, and since near full recovery of added 35SO4 was obtained, initially this fraction is comparable to the L-value. On the other hand, 0.5 M NaHCO3 removed some soil sulphur that was not available to the plants. Liming caused an initial increase in the phosphate extractable fraction, the sulphur seemingly being released from the NaHCO3 extractable fraction, but decreased sulphate sorption also contributed to the increase in S uptake by the plants upon liming