Key Points
- Eight trials over two years compared urea and Sustain. Sustain is urea which contains a urease inhibitor that is designed to reduce gaseous loss of N (volatilisation).
- Both fertilisers were broadcast eight weeks after sowing at three rates (replicated three or four times). Yield response was compared with a control. Soil mineral N at harvest was measured in trials conducted in year 2.
- No advantage to Sustain was found in six of the eight trials. At most of these sites, rain fell within a week of treatments being applied, so there was no benefit to using Sustain over urea to reduce volatilisation.
- At two sites, where dry warm weather prevailed for at least two weeks after application, fully fertilised Sustain plots yielded more than equivalent urea plots. Using current fertiliser prices, this was an economic response.
- Sustain may have benefits over urea when fertiliser N is broadcast in dry conditions, but not where fertiliser N is incorporated (e.g. side-dressed by knifing in) or if rain falls within a few days of broadcasting.