The availability of S in soils can be understood by the interplay among the intensity factor, quantity factor and soil S buffering capacity. The quantity factor is the labile nutrient pool, defined as the quantity present in the soil solid phase, capable of dissolving into the soil solution during one growing cycle of a given annual crop. Aiming to develop a quantification method for labile S, three soils samples were incubated for 60 days after the following treatments: (a) non-disinfected sample, and no S added (-D, -S); disinfected sample, and no S added (+D, -S); non-disinfected sample with S added (-D, +S); disinfected sample with S added (+D, +S). For the labile S determination, 50 x 20 mm of Cl-saturated anionexchange membranes were used. In order to define the labile S determination method, three assays were carried out as follows: (1) extraction with a different number of anion-exchange membranes; (2) successive extractions every 16 h, with one anion-exchange membrane, and (3) extractions at different shaking times (1, 2, 4, 8, 16, 24, 36, 48 and 72 h). Results indicate that the continuous shaking for 48 h and extraction with a single anion-exchange membrane is a feasible and efficient method, extracting a greater proportion of labile S, henceforth termed readily labile sulphur (RLS). The sulphur amount extracted between 48 and 152 h was called slowly labile sulphur (SLS), whereas the not extracted amount of sulphur after 152 h of shaking was labeled non-labile pool (NLS).
readily labile S; slowly labile S; non-labile S; S quantity factor
