Long-term effects of land use and fertilizer treatments on sulfur cycling

The unique archived samples from the Rothamsted Broadbalk Experiment, Engla nd, were used to evaluate long-term effects of changing S inputs from atmos pheric deposition and fertilization on soil S pools and soil S isotope rati o since 1843. The effects of changing land uses were also investigated. Lar ge S inputs from atmospheric deposition and from sulfate fertilizers did no t result in any significant accumulation of soil organic or inorganic S in the arable plots where organic C remained stable. Inputs of sulfate in exce ss of crop uptake were lost mainly through leaching. Organic S accumulated markedly in the arable plot receiving farmyard manure (FYM) or where arable land was allowed to revert to woodland or grassland. In the latter two sys tems soil organic C accumulated faster than organic S. In all soils investi gated the S isotope ratio (delta S-34) decreased substantially during the l ast 150 yr. The decrease in delta S-34 was greater in the woodland, grassla nd, and the arable FYM plot than in other arable plots receiving either ino rganic fertilizers only or no fertilizers. The results indicate that atmosp heric S was more depleted in S-34 than the soil native S at the experimenta l site, and that atmospheric S was incorporated into the organic pool to va rying degrees depending on the C pool. In conclusion,land use had a large e ffect on the S cycling in soils, which is driven mainly by soil organic C c ycling. Without accumulating soil organic C, there appears to be little sco pe for S retention in temperate soils with neutral pH.