SULFUR BALANCES AND S-34 ABUNDANCE IN A LONG-TERM FERTILIZER EXPERIMENT

Reduced SO2 emissions, increased use of non-S-containing fertilizers, and higher crop yields may lead to S deficiency in agricultural soils in the future. In a long-term held experiment on a clay loam soil (Typ ic Eutrochrept) at Uppsala, Sweden, S balances were evaluated for plot s under continuous fallow, plots receiving inorganic fertilizers [(NH4 )(2)(SO4 Or Ca(NO3)(2); 80 kg N ha(-1) yr(-1)], and plots receiving or ganic amendments (2000 kg C ha(-1) yr (-1)) with the aim of estimating plant uptake, leaching losses, immobilization, and variations of delt a(34)S in soil. Total N was correlated with total S concentrations in soil (R(2) = 0.980), but organic C was less well correlated (R(2) = 0. 741). Total soil S decreased in all treatments where no organic materi al was added, the largest decrease occurring in the continuous fallow plots with a S mineralization rate of 6 kg ha(-1) yr(-1). Sulfur added through (NH4)(2)SO4 and sewage sludge was mainly leached, whereas SO4 leaching was reduced in the Ca(NO3)(2)-treated plots as a result of i ncreased crop uptake. Of the organic amendments, 26 to 54% of the S re mained in the soil with a half-life of 24 to 38 yr. Recoveries of S fr om organic amendments in soil were correlated with their initial C/S r atios (R(2) = 0.999) excluding peat. A significant enrichment of S-34 was found only in plots receiving pest. Feat was more highly enriched in S-34 than the other organic materials studied and was more resistan t to decomposition. The results indicate that shifts in soil delta(34) S cannot be used as a tool for quantitative determinations of S turnov er. Nitrogen transformations were the main cause of acidification in t he (NH4)(2)SO4-treated plots, as opposed to S leaching in the sewage-s ludge-treated plots.