Ammonia emissions in combined use of nitrification and urease inhibitors

Combined use of NI and UI [e.g., N-(nbutyl) thiophosphoric triamide (nBPT)] reduced NH3 emission compared with NI treatment only (e.g., Clay et al., 1990; Zaman et al., 2009; Zaman and Blennerhassett, 2010).

Clay et al. (1990) reported that NH3 emission in treating urea with nBPT (8 kg ha−1) and DCD (20 kg ha−1) was around 100 times less than in treating urea with only DCD for bare and residue-covered soil. Zaman et al. (2009) found combined application of nBPT (3 L ha−1) and DCD (7 kg ha−1) reduced NH3 emission by 9 to 78% over urine alone while application of DCD (7 kg ha−1) increased NH3 emission by 9 to 56% over urine alone. Similarity, Zaman and Blennerhassett (2010) found combined application of nBPT (1 L ha−1) and DCD (7 kg ha−1) reduced NH3 emission by 48 to 51% compared with urine alone treatment while only DCD (7 kg ha−1) application increased NH3 emission by 18 to 41% over urine alone.

The reduced NH3 emission by combined application of UI and NI compared with NI application alone can be explained by decreased urea hydrolysis by UI (Singh et al., 2008; Zaman et al., 2009; Zaman and Blennerhassett, 2010). Urease inhibitors decreasing urea hydrolysis retard release of NH4+ from urine and increase in soil pH (e.g., McCarty et al., 1987; Watson et al., 2008; Zaman and Blennerhassett, 2010), both of which are known to accelerate NH3 emission rate (e.g., Nelson, 1982; Francis et al., 2008). These results suggest that combined application of UI and NI can be a solution to prevent increase in NH3 emission by NI treatment and more studies are needed in various climate conditions and soil environments to assess the efficacy.