Table 1 Details of factors used for the assessment of direct nitrous oxide (N 2 O) emission
Primary factor | Break-up of primary factor | Details | Coefficient or value | Remark | |
|---|---|---|---|---|---|
IPCC emission factor | Indian emission factor | ||||
FSN (annual amount of synthetic N-fertilizer applied to soil adjusted for the amount that volatilizes as NH3 and NOx) | NFERT | The total amount of synthetic fertilizer consumed annually [18] | -- | -- | -- |
FracGASF | Fraction of fertilizer volatilize as NH3 and NOX | 10.0% [19] | The difference in the emission factor was due to soil management practices, soil type, pH, climatic condition and also the methodology used for emission assessment [19]. Details of differences in the emission factor due to different methodology used for assessment have been discussed in the Sarkar study [20]. | ||
FAM (annual amount of animal manure nitrogen applied to soils adjusted to account for volatilization of NH3 and NOx) | T | Each defined livestock | -- | -- | For this study four categories were taken, namely, cattle, buffalo, sheep and goat, based on the details available in the Assam statistical handbook[17]. |
N(T) | Number of animals in each category [17] | -- | -- | -- | |
Nex (T) | Annual average nitrogen excretion rate per head for each livestock | Recommended to use country specific factors [19] | Indian emission factor for each livestock category [21] | Nex (T) in g yr-1 = (wet dung excreted by livestock in g day-1)*(dry matter of livestock)*(nitrogen constant of livestock)*365 | |
FracGASM | Fraction of N that volatilizes in NH3 and NOx | 20.0% [19] | 15.0% [8] | -- | |
FracFUEL | Animal manure burnt for fuel | 52.5% [22] | 52.5% [22] | IPCC manual suggested to national study or official statistics of country or region [19] | |
FracPRP | Fraction of animal manure deposited on soil by grazing livestock | Not used in this study | Not used in this study | No data were available | |
FracCOLLEC | Loss during the collection of dung | 30.0% [23] | 30.0% [23] | -- | |
FracFEED | Fraction of animal manure used as feed | 0.0% | 0.0% | Taken as zero, as animal manure is hardly used as feed in India [8] | |
FracCONST | Fraction of animal manure used in construction | 2.0% [22] | 2.0% [22] | -- | |
FBN (amount of nitrogen fixed annually by nitrogen fixing crops) | CropBF | Seed yield of nitrogen fixing crops | Not used in this study | Not used in this study | If seen in terms of area under nitrogen fixing crop in Assam (about 1.23 lakh hectare was under pulses in 2000 to 2001, against gross cropped area of 38.43 lakh hectares) then FBN contribution to total N2O emission may be negligible [17]. However, it is imperative that to have comprehensive source and sink of GHG emission from agriculture sector, which would help in developing better mitigation strategy and policy in the future. This study could not estimate the emission of FBN, due to non-availability of data at district level. |
FracNCRB | Nitrogen content of grain and straw of legumes | Not used in this study | Not used in this study | ||
FCR (amount of nitrogen in crop residues returned to soil annually) | CropST | Amount of straw of non-nitrogen fixing crops incorporated to the soil as residue | Not used in this study | Not used in this study | |
FracNCRST | Nitrogen content of residue of non-nitrogen fixing crops | Not used in this study | Not used in this study | ||
CropSBF | Amount of straw of nitrogen fixing crops incorporated to the soil as residue | Not used in this study | Not used in this study | The gross cropped area in Assam - other than paddy and pulses -under spices, horticulture, vegetable, wheat etcetera, was about 12.74 lakh hectares in 2000 to 2001 [24]. Since crop residue in India is mostly used as fodder or as burning fuel, it is likely that the contribution to N2O emission would not be substantial. However, it is always warranted that if data are made available, the emission inventory would have to be developed in the future. | |
FracNCRSBF | Nitrogen content of residue of nitrogen fixing crops | Not used in this study | Not used in this study | ||
EF1 (kg N2O-N kg-1 N input) | -- | The emission factor for N2O-N emitted from various nitrogen additions in soil | 0.0125 [19] | The N2O emission through nitrification and denitrification in the field, applied with nitrogen fertilizer are strongly influenced by soil temperature, moisture, pH, and soluble organic matter availability [27]. It is to be noted that the IPCC emission factor is taken from the studies of Klemedtssonet al. [28] and Clayton et al. [27], as referenced in the IPCC manual [19]. These studies were done in Europe’s peatland and clay loam grassland soil respectively. The Indian factor is based on the studies of Kumaret al. [25], Majumdar et al. [29] and Pathak et al. [26] which were done in India. It is to be noted that in European and Indian conditions the above-mentioned factors that influence the N2O emission from soil differ markedly, which led to the differing values of emission factors. | |
FOS | -- | Area of organic soil harvested | Not used in this study | Not used in this study | Not an application for Indian conditions, as the organic content in Indian soil varies only from 1% to 5%, while organic soils are those having 12% to 18% organic carbon [8]. |
EF2 | -- | Percent of N2O emissions from organic soil | Not used in this study | Not used in this study | -- |