Equations

Equation 11.1 Direct N2O emissions from managed soils (Tier 1) 11.7

Equation 11.2 Direct N2O emissions from managed soils (Tier 2) 11.10

Equation 11.3 N from organic N additions applied to soils (Tier 1) 11.12

Equation 11.4 N from animal manure applied to soils (Tier 1) 11.13

Equation 11.5 N in urine and dung deposited by grazing animals on pasture, range and paddock (Tier 1) 11.13

Equation 11.6 N from crop residues and forage/pasture renewal (Tier 1) 11.14

Equation 11.7 Dry-weight correction of reported crop yields 11.15

Equation 11.7A Alternative approach to estimate FCR (using Table 11.2) 11.15

Equation 11.8 N mineralised in mineral soils as a result of loss of soil C through change in land use or management (Tiers 1 and 2) 11.16

Equation 11.9 N2O from atmospheric deposition of N volatilised from managed soils (Tier 1) 11.21

Equation 11.10 N2O from N leaching/runoff from managed soils in regions where leaching/runoff occurs (Tier 1) 11.21

Equation 11.11 N2O from atmospheric deposition of N volatilised from managed soils (Tier 2) 11.22

Equation 11.12 Annual CO2 emissions from lime application 11.27

Equation 11.13 Annual CO2 emissions from urea application 11.32

Figures

Figure 11.1 Schematic diagram illustrating the sources and pathways of N that result in direct and indirect N2O emissions from soils and waters 11.8

Figure 11.2 Decision tree for direct N2O emissions from managed soils 11.9

Figure 11.3 Decision tree for indirect N2O emissions from managed soils 11.20

Figure 11.4 Decision tree for identification of appropriate tier to estimate CO2 emissions from liming 11.28

Figure 11.5 Decision tree for identification of appropriate tier to estimate CO2 emissions from urea fertilisation 11.33

Tables

Table 11.1 Default emission factors to estimate direct N2O emissions from managed soils 11.11

Table 11.2 Default factors for estimation of N added to soils from crop residues 11.17

Table 11.3 Default emission, volatilisation and leaching factors for indirect soil N2O emissions 11.24

IIN2O EMISSIONS FROM MANAGED SOILS, AND CO2 EMISSIONS FROM LIME AND UREA APPLICATION

11.1 INTRODUCTION

Chapter 11 provides a description of the generic methodologies to be adopted for the inventory of nitrous oxide (N2O) emissions from managed soils, including indirect N2O emissions from additions of N to land due to deposition and leaching, and emissions of carbon dioxide (CO2) following additions of liming materials and urea-containing fertiliser.

Managed soils1 are all soils on land, including Forest Land, which is managed. For N2O, the basic three-tier approach is the same as used in the IPCC Good Practice Guidance for Land Use, Land-use Change and Forestry (GPG-LULUCF) for Grassland and Cropland, and in the IPCC Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories (GPG2000) for agricultural soils while relevant parts of the GPG-LULUCF methodology have been included for Forest Land. Because the methods are based on pools and fluxes that can occur in all the different land-use categories and because in most cases, only national aggregate (i.e., non-land use specific) data are available, generic information on the methodologies, as applied at the national level is given here, including:

• a general framework for applying the methods, and appropriate equations for the calculations;

• an explanation of the processes governing N2O emissions from managed soils (direct and indirect) and CO2 emissions from liming and urea fertilisation, and the associated uncertainties; and

• choice of methods, emission factors (including default values) and activity data, and volatilisation and leaching factors.

• If activity data are available for specific land-use categories, the equations provided can be implemented for specific land-use categories.

The changes in the 2006 IPCC Guidelines, relative to 1996 IPCC Guidelines, include the following:

• provision of advice on estimating CO2 emissions associated with the use of urea as a fertilizer;

• full sectoral coverage of indirect N2O emissions;

• extensive literature review leading to revised emission factors for nitrous oxide from agricultural soils; and

• removal of biological nitrogen fixation as a direct source of N2O because of the lack of evidence of significant emissions arising from the fixation process.

11.2 n2o emissions from managed soils

This section presents the methods and equations for estimating total national anthropogenic emissions of N2O (direct and indirect) from managed soils. The generic equations presented here can also be used for estimating N2O within specific land-use categories or by condition-specific variables (e.g., N additions to rice paddies) if the country can disaggregate the activity data to that level (i.e., N use activity within a specific land use).

Nitrous oxide is produced naturally in soils through the processes of nitrification and denitrification. Nitrification is the aerobic microbial oxidation of ammonium to nitrate, and denitrification is the anaerobic microbial reduction of nitrate to nitrogen gas (N2). Nitrous oxide is a gaseous intermediate in the reaction sequence of denitrification and a by-product of nitrification that leaks from microbial cells into the soil and ultimately into the atmosphere. One of the main controlling factors in this reaction is the availability of inorganic N in the soil. This methodology, therefore, estimates N2O emissions using human-induced net N additions to soils (e.g., synthetic or organic fertilisers, deposited manure, crop residues, sewage sludge), or of mineralisation of N in soil organic matter following drainage/management of organic soils, or cultivation/land-use change on mineral soils (e.g., Forest Land/Grassland/Settlements converted to Cropland).

1 Managed land is defined in Chapter 1, Section 1.1.

The emissions of N2O that result from anthropogenic N inputs or N mineralisation occur through both a direct pathway (i.e., directly from the soils to which the N is added/released), and through two indirect pathways: (i) following volatilisation of NH3 and NOx from managed soils and from fossil fuel combustion and biomass burning, and the subsequent redeposition of these gases and their products NH4+ and NO3- to soils and waters; and (ii) after leaching and runoff of N, mainly as NO3-, from managed soils. The principal pathways are illustrated in Figure 11.1.

Direct emissions of N2O from managed soils are estimated separately from indirect emissions, though using a common set of activity data. The Tier 1 methodologies do not take into account different land cover, soil type, climatic conditions or management practices (other than specified above). Neither do they take account of any lag time for direct emissions from crop residues N, and allocate these emissions to the year in which the residues are returned to the soil. These factors are not considered for direct or (where appropriate, indirect) emissions because limited data are available to provide appropriate emission factors. Countries that have data to show that default factors are inappropriate for their country should utilise Tier 2 equations or Tier 3 approaches and include a full explanation for the values used.

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