Effect of ammonium thilosulfate and dicyandiamide on residual ammonium in fertilizer bands

Ammonium thiosulfate (ATS, 12–0–0–26S) and dicyandiamide (DCD, 66–0–0) are fertilizer products that also inhibit nitrification. It has also been proposed that ATS can improve the nitrification inhibition properties of DCD. The purpose of this research was to compare the effects of ATS, DCD, and ATS/DCD mixtures on the nitrification of banded urea solution or urea‐ammonium nitrate (UAN) under laboratory, field microplot, and field conditions. The laboratory study demonstrated that adding 8.7% (vol vol‐1) ATS to a urea solution inhibited nitrification by 68%. Inhibition of nitrification was greater with ATS + DCD than with DCD alone. Some nitrite accumulated when ATS was added, but little or no nitrite accumulated when both ATS and DCD were present In field microplot studies, the addition of ATS to urea solution significantly (P ≤ 0.10) increased residual soil ammonium levels over urea alone at six of 11 trials. ATS was usually a less effective nitrification inhibitor than was DCD, and ATS + DCD outperformed DCD at only one of 11 trials. In all three field trials, adding ATS to banded UAN solution led to increased residual ammonium levels. Again, ATS was less effective than DCD or nitrapyrin as a nitrification inhibitor, and no ATS/DCD synergism was observed. It was concluded that the use of ATS as a sulfur fertilizer in fluid fertilizer bands can lead to measurable inhibition of nitrification, but ATS was not as reliable as DCD or nitrapyrin.