Sulfur balances and sulfur-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 (Typic Eutrochrept) at Uppsala, Sweden, S balances were evaluated for plots under continuous fallow, plots receiving inorganic fertilizers [(NH4)(2)(SO4 Or Ca(NO3)(2); 80 kg N ha(-1) yr(-1)], and plots receiving organic amendments (2000 kg C ha(-1) yr (-1)) with the aim of estimating plant uptake, leaching losses, immobilization, and variations of delta(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 material 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 increased crop uptake. Of the organic amendments, 26 to 54% of the S remained in the soil with a half-life of 24 to 38 yr. Recoveries of S from organic amendments in soil were correlated with their initial C/S ratios (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 resistant to decomposition. The results indicate that shifts in soil delta(34)S cannot be used as a tool for quantitative determinations of S turnover. Nitrogen transformations were the main cause of acidification in the (NH4)(2)SO4-treated plots, as opposed to S leaching in the sewage-sludge-treated plots.