Use of nitrification inhibitors

Nitrification inhibitors are often used to increase N fertilizer use efficiency and decrease NO3- losses by leaching and denitrification. There is increasing interest in the use of nitrification inhibitors that effectively block nitrification when applied to soils in conjunction with N fertilizers. In recent years, substantial progress has been made towards understanding the biochemistry of autotrophic NH3 oxidation and the possible modes of action observed with the various inhibitors.

Nitrification inhibitors can effectively reduce N2O emission, and yield is generally higher when inhibitors are applied with N fertilizer. For example, a meta-evaluation of the effectiveness of nitrapyrin (NP) in the mid-West of the US showed that, on average, NP combined with N fertilizer led to higher crop yield (7 per cent), increased soil N retention (28 per cent), less nitrate leaching (-16 per cent) and 51 per cent lower N2O emissions compared to fields receiving N fertilizer without NP (Wolt, 2004). Alternative nitrification inhibitors such as DCD (dicyandiamide), ATS (ammonium thiosulphate) and DMPP (3,4-dimethyl pyrazole phosphate) can be expected to have a similar effect on N2O emission. Research conducted recently in New Zealand showed that strategic application of a nitrification inhibitor to pasture, following simulated urine excretion by grazing dairy cattle, significantly reduced direct (-67 per cent) and indirect (-74 per cent) N2O emissions over extensive periods (Kelliher et al, 2007). However, the performance of any of these nitrification inhibitors depends on physico-chemical properties, efficacy and persistence in various environments and management practices. Their use and performance in livestock systems are discussed in more detail in Chapter 6.

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