The decision tree for estimating direct N₂O emissions from agricultural soils outlines the steps Parties should follow (see Figure 4.7 in the IPCC Good Practice Guidance).

The main features of this decision tree are:

• If there is no nitrogen input to soils, no nitrogen-fixing crops are produced, and no histosols are cultivated then the Party should report “not occurring” (NO);
• If the sub-category is not key, emissions can be estimated using the Tier 1a or the Tier 1b methods, FAO activity data, and default emission factors and partition fractions;
• If direct emissions from agricultural soils is a key category, and the nitrogen input is a significant source, Parties should collect country-specific activity data for individual contributions of nitrogen and make efforts to obtain rigorously documented country-specific partition fractions and emission factors.  However, if no country-specific partition fractions and/or emission factors are available default partition fractions and/or emission factors may be used.