S-Benzylisothiouronium Derivatives as Nitrification Inhibitors

Series of S-benzylisothiouronium derivatives have been synthesized and evaluated for nitrification inhibitory activity under laboratory conditions. S-Benzyiisothiouronium chloride and its formic, acetic, chloroacetic, propanoic, butanoic, pentanoic, benzoic and furoic acid derivatives showed significant nitrification inhibitory activity. At 20% dose, the furoate showed 33.5% nitrification inhibition (NI) on 56th day of incubation in comparison with 47.6% in 5% nitrapyrin. At 5 and 20% doses, the furoate exhibited 50.3 and 74.2% NI on the 15th, 41.6 and 60.5% on the 28th and 16.2 and 41.7% on the 42nd day respectively. Based on concentration of ammonium and nitrate-N, percentage nitrification inhibition (NI), ratio of ammonium to nitrate-N and total mineral-N, the furoate showed the highest relative efficiency after nitrapyrin through out the 56-day incubation. The mentioned nine active compounds were less effective than nitrapyrin but better than dicyandiamide (DCD), particularly at higher doses. The S-benzylisothiouronium butanoate showed better relative efficiency than DCD even at 5% dose during the entire period and both S-benzylisothiouronium furoate and propanoate performed better than DCD at 5% dose up to 42nd day.