Indirect N2O emissions

In addition to the direct emissions of N2O from managed soils that occur through a direct pathway (i.e., directly from the soils to which N is applied), emissions of N2O also take place through two indirect pathways (as illustrated above in Section 11.2).

The first of these pathways is the volatilisation of N as NH3 and oxides of N (NOx), and the deposition of these gases and their products NH4+ and NO3- onto soils and the surface of lakes and other waters. The sources of N as NH3 and NOx are not confined to agricultural fertilisers and manures, but also include fossil fuel combustion, biomass burning, and processes in the chemical industry (see Volume 1, Chapter 7, Section 7.3). Thus, these processes cause N2O emissions in an exactly analogous way to those resulting from deposition of agriculturally derived NH3 and NOx, following the application of synthetic and organic N fertilisers and /or urine and dung deposition from grazing animals. The second pathway is the leaching and runoff from land of N from synthetic and organic fertiliser additions, crop residues 18, mineralisation of N associated with loss of soil C in mineral and drained/managed organic soils through land-use change or management practices, and urine and dung deposition from grazing animals. Some of the inorganic N in or on the soil, mainly in the NO3- form, may bypass biological retention mechanisms in the soil/vegetation system by transport in overland water flow (runoff) and/or flow through soil macropores or pipe drains. Where NO3- is present in the soil in excess of biological demand, e.g., under cattle urine patches, the excess leaches through the soil profile. The nitrification and denitrification processes described at the beginning of this chapter transform some of the NH4+ and NO3- to N2O. This may take place in the groundwater below the land to which the N was applied, or in riparian zones receiving drain or runoff water, or in the ditches, streams, rivers and estuaries (and their sediments) into which the land drainage water eventually flows.

This methodology described in this Chapter addresses the following N sources of indirect N2O emissions from managed soils arising from agricultural inputs of N:

• synthetic N fertilisers (FSN);

• organic N applied as fertiliser (e.g., applied animal manure 19, compost, sewage sludge, rendering waste and other organic amendments) (FON);

• urine and dung N deposited on pasture, range and paddock by grazing animals (FPRP);

• N in crop residues (above- and below-ground), including N-fixing crops and forage/pasture renewal returned to soils (Fcr) 20; and

• N mineralisation associated with loss of soil organic matter resulting from change of land use or management on mineral soils (FSOM).

The generic Tier 1 and Tier 2 methods described below can be used to estimate aggregate total indirect N2O emissions from agricultural N additions to managed soils for an entire country. If a country is estimating its direct N2O from managed soils by land-use category, the indirect N2O emissions can also be estimated by the same disaggregation of land-use categories using the equations presented below with activity data, partitioning fractions, and/or emission factors specific for each land-use category. The methodology for estimating indirect N2O emissions from combustion-related and industrial sources is described in Volume 1, Chapter 7, Section 7.3.

11.2.2.1 Choice of method

Refer to the decision tree in Figure 11.3 (Indirect N2O Emissions) for guidance on which Tier method to use.

18 The inclusion of crop residues as an N input into the leaching and runoff component is a change from the previous IPCC Guidelines.

19 Volatilisation and subsequent deposition of nitrogen from the manure in manure management systems is covered in the manure management section of this Volume.

20 Nitrogen from these components is only included in the leaching/run-off component of indirect N2O emission.

Figure 11.3 Decision tree for indirect N2O emissions from managed soils

Figure 11.3 Decision tree for indirect N2O emissions from managed soils

Policy Factors

Note:

1: N sources include: synthetic N fertilizer, organic N additions, urine and dung depositions, crop residue, N mineralization/immobilization associated with loss/gain of soil C on mineral soils as a result of land use change or management practices (crop residue and N mineralization/immobilization is only accounted for in the indirect N2O emissions from leaching/runoff). Sewage sludge or other organic N additions can be included if sufficient information is available.

2: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

3: As a rule of thumb, a sub-source category would be significant if it accounts for 25-30% of emissions from the source category.

Tier 1

Volatilisation, N2O(ATD)

The N2O emissions from atmospheric deposition of N volatilised from managed soil are estimated using Equation 11.9:

Equation 11.9

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

N2O( ATD) -N = [(( • FracGASF ) + {{FON + FPRP ) • FracGASM )J • EF4

Where:

N2O(ATD)-N = annual amount of N2O-N produced from atmospheric deposition of N volatilised from managed soils, kg N2O-N yr-1

Fsn = annual amount of synthetic fertiliser N applied to soils, kg N yr-1

FracGASF = fraction of synthetic fertiliser N that volatilises as NH3 and NOx, kg N volatilised (kg of N applied)-1 (Table 11.3)

FON = annual amount of managed animal manure, compost, sewage sludge and other organic N additions applied to soils, kg N yr-1

Fprp = annual amount of urine and dung N deposited by grazing animals on pasture, range and paddock, kg N yr-1

FracGASM = fraction of applied organic N fertiliser materials (FON) and of urine and dung N deposited by grazing animals (FPRP) that volatilises as NH3 and NOx, kg N volatilised (kg of N applied or deposited)-1 (Table 11.3)

EF4 = emission factor for N2O emissions from atmospheric deposition of N on soils and water surfaces, [kg N-N2O (kg NH3-N + NOx-N volatilised)-1] (Table 11.3)

Conversion of N2O(ATD)-N emissions to N2O emissions for reporting purposes is performed by using the following equation:

Leaching/Runoff N2O(L)

The N2O emissions from leaching and runoff in regions where leaching and runoff occurs are estimated using Equation 11.10:

Equation 11.10

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

N 2O( l) -N = ((SN + FON + FPRP + FCR + FSOM )• FracLEACH-(H) • EF5

Where:

N2O(L)-N = annual amount of N2O-N produced from leaching and runoff of N additions to managed soils in regions where leaching/runoff occurs, kg N2O-N yr-1

FSN = annual amount of synthetic fertiliser N applied to soils in regions where leaching/runoff occurs, kg N yr-1

FON = annual amount of managed animal manure, compost, sewage sludge and other organic N additions applied to soils in regions where leaching/runoff occurs, kg N yr-1

Fprp = annual amount of urine and dung N deposited by grazing animals in regions where leaching/runoff occurs, kg N yr-1 (from Equation 11.5)

Fcr = amount of N in crop residues (above- and below-ground), including N-fixing crops, and from forage/pasture renewal, returned to soils annually in regions where leaching/runoff occurs, kg N yr-1

Fsom = annual amount of N mineralised in mineral soils associated with loss of soil C from soil organic matter as a result of changes to land use or management in regions where leaching/runoff occurs, kg N yr-1 (from Equation 11.8)

FracLEACH-(H) = fraction of all N added to/mineralised in managed soils in regions where leaching/runoff occurs that is lost through leaching and runoff, kg N (kg of N additions)-1 (Table 11.3)

EF5 = emission factor for N2O emissions from N leaching and runoff, kg N2O-N (kg N leached and runoff)-1 (Table 11.3)

Note: If a country is able to estimate the quantity of N mineralised from organic soils, then include this as an additional input to Equation 11.10.

Conversion of N2O(L)-N emissions to N2O emissions for reporting purposes is performed by using the following equation:

Tier 2

If more detailed emission, volatilisation or leaching factors are available to a country than are presented in Table 11.3, further disaggregation of the terms in the equations can also be undertaken. For example, if specific volatilisation factors are available for the application of synthetic fertilisers (FSN) under different conditions i, Equation 11.9 would be expanded to become 21:

Equation 11.11

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

N2O(ATD)-N = \ Z {TsNi • FracGASF, )+[ + FPRP ) • FraCGASM ] r • EF4

Where:

N2O(ATD)-N = annual amount of N2O-N produced from atmospheric deposition of N volatilised from managed soils, kg N2O-N yr-1

FSNi = annual amount of synthetic fertiliser N applied to soils under different conditions i, kg N yr-1

FracGAsF. = fraction of synthetic fertiliser N that volatilises as NH3 and NOx under different conditions i, kg N volatilised (kg of N applied)-1

FON = annual amount of managed animal manure, compost, sewage sludge and other organic N additions applied to soils, kg N yr-1

FPRP = annual amount of urine and dung N deposited by grazing animals on pasture, range and paddock, kg N yr-1

FracGAsM = fraction of applied organic N fertiliser materials (FON) and of urine and dung N deposited by grazing animals (FPRP) that volatilises as NH3 and NOx, kg N volatilised (kg of N applied or deposited)-1 (Table 11.3)

EF4 = emission factor for N2O emissions from atmospheric deposition of N on soils and water surfaces, [kg N-N2O (kg NH3-N + NOx-N volatilised)-1] (Table 11.3)

Note: If a country is able to estimate the quantity of N mineralised from drainage/management of organic soils then include this as one of the N inputs into the Tier 2 modification of Equation 11.10.

Conversion of N2O(ATD)-N emissions to N2O(ATD) emissions for reporting purposes is performed by using the following equation:

21 It is important to note that Equation 11.11 is just one of many possible modifications to Equation 11.9, and is also meant to illustrate how Equation 11.10 could be modified, when using the Tier 2 method. The eventual form of Equation 11.11 will depend upon the availability of land use and/or condition-specific partitioning fractions and/or emission factors and the ability to which a country can disaggregate its activity data.

Tier 3

Tier 3 methods are modelling or measurement approaches. Models are useful as they can relate the variables responsible for the emissions to the size of those emissions. These relationships may then be used to predict emissions from whole countries or regions for which experimental measurements are impracticable. For more information refer to Chapter 2, Section 2.5, where guidance is given that provides a sound scientific basis for the development of a Tier 3 Model-based Accounting System.

11.2.2.2 Choice of emission, volatilisation and leaching

FACTORS

The method for estimating indirect N2O emissions includes two emission factors: one associated with volatilised and re-deposited N (EF4), and the second associated with N lost through leaching/runoff (EF5). The method also requires values for the fractions of N that are lost through volatilisation (FracGASF and FracGASM) or leaching/runoff (FracLEACH-(H)). The default values of all these factors are presented in Table 11.3.

Note that in the Tier 1 method, for humid regions or in dryland regions where irrigation (other than drip irrigation) is used, the default FracLEACH-(H) is 0.30. For dryland regions, where precipitation is lower than evapotranspiration throughout most of the year and leaching is unlikely to occur, the default FracLEACH is zero. The method of calculating whether FracLEACH-(H) = 0.30 should be applied is given in Table 11.3.

Country-specific values for EF4 should be used with great caution because of the special complexity of transboundary atmospheric transport. Although inventory compilers may have specific measurements of N deposition and associated N2O flux, in many cases the deposited N may not have originated in their country. Similarly, some of the N that volatilises in their country may be transported to and deposited in another country, where different conditions that affect the fraction emitted as N2O may prevail. For these reasons the value of EF4 is very difficult to determine, and the method presented in Volume 1, Chapter 7, Section 7.3 attributes all indirect N2O emissions resulting from inputs to managed soils to the country of origin of the atmospheric NOx and NH3, rather than the country to which the atmospheric N may have been transported.

11.2.2.3 Choice of activity data

In order to estimate indirect N2O emissions from the various N additions to managed soils, the parameters FSN, Fon, Fprp, Fcr, Fsom need to be estimated.

Applied synthetic fertiliser (FSN)

The term FSN refers to the annual amount of synthetic fertiliser N applied to soils. Refer to the activity data section on direct N2O emissions from managed soils (Section 11.2.1.3) and obtain the value for FSN.

Applied organic N fertilisers (FON)

The term FON refers to the amount of organic N fertiliser materials intentionally applied to soils. Refer to the activity data section on direct N2O emissions from managed soils (Section 11.2.1.3) and obtain the value for FON.

Urine and dung from grazing animals (FPRP)

The term FPRP refers to the amount of N deposited on soil by animals grazing on pasture, range and paddock. Refer to the activity data section on direct N2O emissions from managed soils (Section 11.2.1.3) and obtain the value for FPRP.

Crop residue N, including Nfrom N-fixing crops and forage/pasture renewal, returned to soils (FCR)

The term FCR refers to the amount of N in crop residues (above- and below-ground), including N-fixing crops, returned to soils annually. It also includes the N from N-fixing and non-N-fixing forages mineralised during forage/pasture renewal. Refer to the activity data section on direct N2O emissions from managed soils (Section 11.2.1.3) and obtain the value for FCR.

Mineralised N resulting from loss of soil organic C stocks in mineral soils (FSOM)

The term FSOM refers to the amount of N mineralised from the loss of soil organic C in mineral soils through land-use change or management practices. Refer to the activity data section on direct N2O emissions from managed soils (Section 11.2.1.3) and obtain the value for FSOM.

Table 11.3

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

Factor

Default value

Uncertainty range

EF4 [N volatilisation and re-deposition], kg N2O-N (kg NH3-N + NOx-N volatilised)"1 22

0.010

0.002 - 0.05

EF5 [leaching/runoff], kg N2O-N (kg N leaching/runoff) -1 23

0.0075

0.0005 -0.025

FracGASF [Volatilisation from synthetic fertiliser], (kg NH3-N + NOx-N) (kg N applied) -1

0.10

0.03 - 0.3

FracGASM [Volatilisation from all organic N fertilisers applied , and dung and urine deposited by grazing animals], (kg NH3-N + NOx-N) (kg N applied or deposited) -1

0.20

0.05 - 0.5

FracLEACH"(H) [N losses by leaching/runoff for regions where S(rain in rainy season) - S (PE in same period) > soil water holding capacity, OR where irrigation (except drip irrigation) is employed], kg N (kg N additions or deposition by grazing animals)-1

0.30

0.1 - 0.8

Note: The term FracLEACH previously used has been modified so that it now only applies to regions where soil water-holding capacity is exceeded, as a result of rainfall and/or irrigation (excluding drip irrigation), and leaching/runoff occurs, and redesignated as FracLEACH-(H). In the definition of FracLEACH-(H) above, PE is potential evaporation, and the rainy season(s) can be taken as the period(s) when rainfall > 0.5 * Pan Evaporation. (Explanations of potential and pan evaporation are available in standard meteorological and agricultural texts). For other regions the default FracLEACH is taken as zero.

11.2.2.4 Uncertainty assessment

Uncertainties in estimates of indirect N2O emissions from managed soils are caused by uncertainties related to natural variability and to the emission, volatilization and leaching factors (see Table 11.3 for uncertainty ranges), activity data, and lack of measurements. Additional uncertainty will be introduced in an inventory when values for these factors that are not representative of all conditions in a country are used. In general, the reliability of activity data will be higher than that of the emission, volatilisation and leaching factors. As with direct emissions, further uncertainties may be caused by missing information on observance of laws and regulations related to handling and application of fertiliser and manure, and changing management practices in farming. Generally, it is difficult to obtain information on the actual observance of laws and possible emission reductions achieved as well as information on farming practices. Uncertainties in emission factors are nevertheless likely to dominate and uncertainty ranges are indicated in the tabulations above. For more detailed guidance on uncertainty assessment refer to Volume 1, Chapter 3.

22 The uncertainty range has been widened, in view of results showing that emissions from some environments, particularly deciduous forests receiving high rates of N deposition from the atmosphere, are substantially higher than those previously reported (e.g., Butterbach-Bahl et al., 1997; Brumme et al., 1999; Denier van der Gon and Bleeker, 2005)., while there is also clear evidence that EFs can be very low (<< 0.01) in low-deposition environments (e.g., Corre et al., 1999). The mean value of 0.01 has been retained, because it coincides with the revised EF for direct emission from managed land (see Table 11.1 above), and it is recognised that in many countries a substantial fraction of the indirect emissions will in fact originate from managed land.

23 The overall value for the emission factor for leached N (EF5) has been changed from 0.025 to 0.0075 kg N2O-N/kg N leached/ in runoff water. This emission factor incorporates three components: EF5g, EF5r and EF5e, which are the emission factors for groundwater and surface drainage, rivers, and estuaries, respectively. Recent results indicate that the previously used emission factor for groundwater and surface drainage (0.015) was too high and should be reduced to 0.0025 kg N2O-N/kg mineral N (mainly nitrate) leached (Hiscock et al., 2002, 2003; Reay et al., 2004, 2005; Sawamoto et al., 2005). The emission factor for rivers has also been reduced from 0.0075 kg N2O-N/kg N to the same value, 0.0025 kg N2O-N/kg N in the water. This is in recognition that while still lower mean values (of the order of 0.0003 to 0.0005) have been reported by, e.g., Dong et al., (2004) and Clough et al , (2006) for relatively short river systems, there remains the possibility that higher values than those obtained by these authors apply to longer river systems. The value for estuaries remains at 0.0025 kg N2O-N/kg N.

Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

Get My Free Ebook


Post a comment