Keywords: Ammonium nitrate, urea, urease inhibitors, ammonia emissions, crop N uptake efficiency.
Ammonium nitrate (AN) is the main source of manufactured nitrogen (N) fertiliser used in the UK. Urea-based N (in solid urea and as liquid urea ammonium nitrate – UAN) has accounted for typically 15% of total N use, although use has increased closer to 20% in recent years. Since AN has potentially explosive properties and to address UK national security issues, wide ranging research (2002-2005) was carried out to investigate the suitability of urea-N, rather than AN, for agriculture. The potential loss of ammonia was the main agronomic and environmental issue addressed. Ammonia loss measurements using wind tunnels showed that the average ammonia emission factor (EF, % of N applied) from granular urea was 27% (range 10-58%) at 15 grassland experiments, and 22% (range 2 to 43%) at 13 winter cereal experiments. The average ammonia EF from AN was less than 3%. Ammonia emissions from liquid UAN were intermediate between granular urea and AN. Use of the urease inhibitor nBTPT (trade name Agrotain ®) reduced ammonia emissions from granular urea by c. 70%, and by c.40% from liquid UAN. Rainfall (15 mm) following granular urea application reduced ammonia emissions, but there was no consistent effect of crop height, land use (grass or tillage crops) or soil type. Crop response experiments showed that an extra c. 20% of urea-N was needed to achieve the same cereal crop yield and quality as from the use of AN. At an application rate of 220 kg N/ha, use of urea consistently resulted in a lower grain yield (mean of c. 0.3 t/ha) and lower grain protein content (mean of c. 0.3% at 100% DM) than from AN. The research showed that ammonia losses from urea-based fertilisers are variable, unpredictable and can be large, but that addition of the urease inhibitor nBTPT is a potentially valuable mitigation method.
Brian Chambers, ADAS Gleadthorpe, Meden Vale, Mansfield, Nottingham, NG20 9PF, UK.
Peter Dampney, ADAS Boxworth, Boxworth, Cambridge CB23 4NN, UK.
20 pages, 6 figures, 6 tables, 8 references.