Persistence of nitrification inhibitors and their efficacy to reduce nitrous oxide emissions from contrasting pasture soils amended with urine

Abstract
Nitrification inhibitors (NIs) play a key role in mitigating nitrogen (N) losses from pastoral agricultural systems. The effect of NI, dicyandiamide (DCD) on reducing nitrous oxide (N2O) emissions from urine patches on pasture soils is well-documented. But information on the comparative effectiveness of other most used NIs [3,4-dimethylpyrazole phosphate (DMPP), 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) and A2 (a confidential NI)] is lacking.  Therefore, laboratory incubation experiments were conducted to test the persistence of DMPP, nitrapyrin and A2 (using DCD as a reference NI) and assess their effectiveness to mitigate N2O emissions from two urine-treated pasture soils (Te Kowhai and Tokomaru soils) varying in texture and organic matter.  The half-life values (at 15°C) of the NIs varied with soil organic matter and clay content, and were 69-87 days for DMPP, 18-29 days for nitrapyrin and 20-33 days for DCD. All the inhibitors reduced N2O emissions, but their effectiveness differed with the amount of inhibitor and soil type. The reductions in N2O emission were 19-48% with DMPP, 48-59% with nitrapyrin, 12-43% with A2 and 45-47% with DCD. Higher rates of both nitrapyrin and A2 achieved significantly (p ? 0.05) greater reductions on the Tokomaru soil than on the Te Kowhai soil. There was no effect of NIs on the levels of soil microbial biomass carbon and nitrogen (MBC and MBN) during the study period.  
