Potential of ammonium thiosulfate and potassium thiosulfate to inhibit nitrification in soils

Abstract

Nitrogen use efficiency by crops can vary according to soil properties and environmental conditions. Nitrification inhibitors show potential to improve efficiency of fertilizer N use by keeping N in the ammonium form, decreasing leaching, and denitrification. The objective of this study was to evaluate the effectiveness of ammonium thiosulfate (ATS) and potassium thiosulfate (KTS) products to inhibit nitrification in three soils: 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 two rates of ATS and KTS (3.54:1 and 7.68:1 N:S ratio) to inhibit nitrification of urea-based fertilizers compared to an untreated control, urea, urea + ammonium sulfate, and urea + dicyandiamide (DCD) treatments. The higher rate of ATS and KTS reduced nitrification by 75% compared to untreated urea from day 14 to 63 in the Tujunga loamy sand in the first run and by 80% from day 21 to 56 in run two. Similarly, the higher rate of ATS and KTS reduced nitrification by 40% compared to urea for the Sable silt loam in run one from day 42 to 70. No treatments reduced nitrification compared to untreated urea in the Marvyn loamy sand. Nitrite-N concentrations followed similar trends when compared to NO₃⁻-N in the Tujunga soil, suggesting that the treatments inhibiting nitrification are inhibiting the first step in the nitrification process. Both ATS and KTS were shown to inhibit nitrification comparable to DCD, but effectiveness of these inhibitors need to be evaluated further in different soils.