Aggregate Associated Sulfur Fractions in Long‐Term (>80 Years) Fertilized Soils

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Understanding soil sulfur pools and associated aggregates S fractions can provide a platform for monitoring S dynamics in soils. A long‐term experiment established in 1922 on an Aquic Eutrocryepts in South‐eastern Norway was chosen to investigate the effects of long‐term fertilization on S fractions in bulk soil and those associated with aggregates. Chloroform fumigation‐extraction was used to determine Microbial biomass S (MBS) and the wet chemical analysis method was used to fractionate soil S into ester S (hydriodic acid reducible S), carbon‐bonded S (Raney nickel reducible S) and residual S (Raney nickel non‐reducible S). High farmyard manure (FYM) application resulted in higher MBS in bulk soil than nitrogen + potassium (NK) application, but it did not differ significantly from the control. Application of FYM at 60 Mg ha −1 resulted into accumulation of total S, total organic S and carbon‐bonded S in bulk soils, while mineral fertilizer (nitrogen+phosphorus+potassium+sulfur [NPKS] and NK) and the medium rate of FYM did not increase the accumulation of total S and organic S fractions. The macroaggregate sizes (>2 and 1–2 mm) and the finest aggregate size (<0.106 mm) showed significantly greater total S concentration than other aggregate sizes. Ester S and residual S were predominant organic S fractions and they accounted for 39 to 52% and 38 to 51% of the organic S, respectively. The macroaggregate sizes (>2 and 1–2 mm) contained the highest ester S, but microaggregates (<0.106 mm) exhibited higher carbon‐bonded S and residual S than other aggregates. In conclusion, the accumulation of S was dependent on fertilizer type, the rate of FYM application and aggregate sizes.