An inventory of nitrous oxide emissions from agriculture in the UK using the IPCC methodology: emission estimate, uncertainty and sensitivity analysis

Nitrous oxide emission from UK agriculture was estimated, using the IPCC de fault Values of all emission factors and parameters, to be 87 Gg N2O-N in b oth 1990 and 1995. This estimate was shown, however, to have an overall unc ertainty of 62%. The largest component of the emission (54%) was from the d irect (soil) sector. Two of the three emission factors applied within the s oil sector, EF1 (direct emission from soil) and EF3(PRP) (emission from pas ture range and paddock) were amongst the most influential on the total esti mate, producing a +/- 31 and + 11% to -17% change in emissions, respectivel y, when varied through the IPCC range from the default value. The indirect sector (from leached N and deposited ammonia) contributed 29% of the total emission, and had the largest uncertainty (126%). The factors determining t he fraction of N leached (Frac(LEACH)) and emissions from it (EF5), were th e two most influential. These parameters are poorly specified and there is great potential to improve the emission estimate for this component. Use of mathematical models (NCYCLE and SUNDIAL) to predict Frac(LEACH) suggested that the IPCC default value for this parameter may be too high fol most sit uations in the UK. Comparison with other UK-derived inventories suggests that the IPCC methodo logy may overestimate emission. Although the IPCC approach includes additio nal components to the other inventories (most notably emission from indirec t sources), estimates for the common components (i.e. fertiliser and animal s), and emission factors used, are higher than those of other inventories. Whilst it is recognised that the IPCC approach is generalised in order to a llow widespread applicability, sufficient data are available to specify at least two of the most influential parameters, i.e. EF1 and Frac(LEACH), mor e accurately, and so provide an improved estimate of nitrous oxide emission s from UK agriculture. (C) 2001 Elsevier Science Ltd. All rights reserved.