Ammonium Thiosulfate and Potassium Thiosulfate as Potential Nitrification Inhibitors in Soils

Abstract

Nitrogen use efficiency (NUE) can vary according to soil properties, precipitation, and soil temperature. Nitrification inhibitors show potential to increase NUE by decreasing the amount of N lost from leaching and denitrification, keeping N in an ammonium form. The objective of this study was to evaluate the effectiveness of ammonium thiosulfate (ATS) and potassium thiosulfate (KTS) products to inhibit nitrification in three soil types: Marvyn loamy sand, Tujunga loamy sand, and Sable silt loam. Two runs of a 10-week incubation experiment were performed, and soil ammonium-N (NH4+-N), nitrite-N (NO2--N), and nitrate-N (NO3--N) concentrations were measured to determine the effectiveness of ATS and KTS to inhibit nitrification in urea-based fertilizers compared to an untreated control, urea, urea + ammonium sulfate, and urea + dicyandiamide (DCD) treatments. Incubation results showed that the higher thiosulfate rate of ATS and KTS reduced nitrification compared to urea alone and urea + DCD in the Tujunga loamy sand from day 21 to day 63 in the first run and from day 28 to day 56 in the second run. Within the Sable silt loam soil, the higher thiosulfate rate in ATS and KTS were similar to urea + DCD in reducing nitrification from day 35 to day 56 in the first run, but no treatment differences were seen in run two. No treatments reduced nitrification compared to the untreated urea treatment in the Marvyn loamy sand soil type. Trends for NO2--N concentrations corresponded to trends for NO3--N concentrations in the Tujunga soil, showing the treatments inhibiting nitrification are most likely inhibiting the first step in the nitrification process. Greenhouse studies on corn (Zea mays L.) were conducted to determine effects on plant growth and soil NH4+-N and NO3--N. All fertilizer treatments in all soil types resulted in higher NH4+-N compared to the control from day 0 to day 7 in run one and from day 0 to day 14 in run two. Nitrate-N concentrations in run one tended to be higher in all fertilizer treatments than the control in the Marvyn and Tujunga soil from day 0 until day 14, but no differences were seen in the Sable silt loam. However, treatment did not influence NO3--N concentrations in the second run. Overall, ATS, KTS and DCD reduced nitrification compared to urea in the Tujunga loamy sand in both incubation runs and Sable silt loam in one out of two runs for the incubation studies. However, similar results were not observed in the greenhouse studies. Both ATS and KTS have potential to inhibit nitrification, but effectiveness of these inhibitors is dependent on soil type and climatic conditions.