INFLUENCE OF THIOSULFATE ON NITRIFICATION, DENITRIFICATION, AND PRODUCTION OF NITRIC-OXIDE AND NITROUS-OXIDE IN SOIL

Thiosulfate and CS2 inhibit nitrification. The effect of the addition of thiosulfate on the turnover of inorganic N compounds was tested in an Egyptian and a German arable soil under nitrifying and denitrifying conditions. For nitrification, the soils were amended with and incuba ted under aerobic conditions. For denitrification, the soils were amen ded with NH4+ and incubated under anaerobic conditions. For denitrific ation, the soils were amended with No-3(-) and incubated under anaerob ic conditions. In both cases, the thiosulfate decreased with time whil e tetrathionate accumulated to an intermediate extent. Both compounds disappeared completely after <25 days. Production of CS2 was not obser ved. Carbonyl sulfide was produced only in the Egyptian soil, but prod uction decreased with increasing amounts of added thiosulfate. Under n itrifying conditions, the addition of increasing amounts of thiosulfat e (25, 50, and 100 mu g S g(-1) dry weight) resulted in decreasing rat es of NH4+ oxidation to NO3-; it also resulted in an increasing interm ediate accumulation of NO2- and NO, and in an increasing production of N2O. Under denitrifying conditions, the addition of increasing amount s of thiosulfate did not significantly affect the rate of NO3- reducti on, and resulted in an increasing intermediate accumulation of NO2- an d of NO only in the German soil in which the production of N2O was sli ghtly inhibited by thiosulfate. These results demonstrate that the nit rification of NH4+ and NO2- was inhibited by increasing concentrations of thiosulfate and/or tetrathionate without involving the formation o f volatile S compounds as potential nitrification inhibitors. Denitrif ication was not affected by the addition of thiosulfate.