The effect of nitrification inhibitors on wheat crop performance on coarse-grained soils in Mediterranean environments

Elliott Duncan1,2*, Cathryn O’Sullivan1, Margaret Roper1 and Mark Peoples3

 1 CSIRO Agriculture, Centre for Environment and Life Sciences, Underwood Avenue, Floreat WA 6014, Australia.

2 Future Industries Institute, University of South Australia, Mawson Lakes Campus, Mawson Lakes, SA 5095, Australia.

3 CSIRO Agriculture, Black Mountain Laboratories, Acton, ACT 2601, Australia.

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This research investigates whether nitrification inhibitors (NIs), including DMPP, DCD & nitrapyrin, are effective in preserving ammonium (NH4+) in soil, reducing the abundance of ammonia oxidising microorganisms in soil and improving crop performance in Mediterranean wheat cropping systems. Data from laboratory soil incubation studies and glasshouse pot trials demonstrated that, under controlled conditions, DMPP was highly effective at inhibiting nitrification and limiting the growth of ammonia oxidising bacteria (AOB) for over 100 days on coarse-grained soils common in the Western Australian wheatbelt. This, however, did not result in improvements in grain yield or quality in wheat (Triticum aestivum) cv. Mace which suggests that preservation of mineral N as NH4+ does little for crop N uptake. Under field conditions yield increases of ≈300 kg ha-1 were observed in the presence of DMPP in a small number of trials. These increases, however, only occurred on soils with a shallow coarse-grained layer (<30cm) over a heavy clay pan. It is likely that the clay layer in these soils slowed the movement of water (and N) thus allowing the crop access to fertiliser N for a longer period of time.  Overall, this study demonstrates that NIs slow nitrification in a range of soils common in the study region and in some cases yield and NUE benefits can occur.