# The Evolutionary Traits of Carbon Emissions from the Planting Industry in Beijing, China
## 2 Materials and Methods
### Data Sources and Calculation Methods
#### 2.2.2 Carbon Emissions of N2O from Agricultural Land  
Carbon emissions of N2O from farmland are mainly caused by nitrogen-containing substances entering farmland soil, resulting in N2O emissions from farmland. The N2O emissions from farmland are mainly divided into direct carbon emissions and indirect carbon emissions. The direct emissions refer to the carbon emissions of N2O caused by returning straw to the field, the use of nitrogen-containing chemical fertilizers, and returning livestock and poultry manure to the field. The indirect carbon emissions mainly refer to the N2O emissions caused by two aspects: soil nitrogen leaching and runoff, and atmospheric ammonia deposition. The formula is as follows:  
\[\mathrm{C_{N2O}=D_{N2O}+I_{N2O}}\]  
The direct N2O carbon emissions from agricultural land are caused by three factors: nitrogen-containing fertilizer input, organic fertilizer being returned to the field, and crop straw being returned to the field. The accounting formula is as follows:  
\[\mathrm{D_{N2O}=F_{N2O}+O_{N2O}+S_{N2O}}\]  
Among them, FN2O is the soil N2O carbon emissions caused by the input of nitrogen-containing fertilizer, including nitrogen fertilizer and compound fertilizer; ON2O is the soil N2O carbon emissions caused by organic fertilizer being returned to fields; and SN2O is the soil N2O carbon emissions caused by crop straw being returned to the field. The calculation formula for the direct carbon emissions of N2O caused by nitrogen-containing chemical fertilizers is as follows:  
\[\mathrm{F_{N2O}=(N_{w}+C_{w}\times W_{0})\times E_{N}\times 298}\]  
Among them, N\({}_{w}\) is the pure equivalent of nitrogen fertilizer application; C\({}_{w}\) is the pure equivalent of agricultural compound fertilizer application; W\({}_{0}\) is the mass fraction of nitrogen in the chemical fertilizer, which is 28.41% [34]; E\({}_{N}\) is the direct emissions coefficient of N2O from agricultural land, which is 0.0057 kg N2O-N-per unit of N input [31] (the same below); and 298 is the global warming potential of N2O [35] (the same below). The calculation formula for the direct carbon emissions of N2O caused by the return of organic fertilizers to the field is as follows: \begin{table}
\begin{tabular}{c c c c} \hline
**Agricultural Inputs** & **Carbon Emissions** & **Unit (Calculated** & **Data Sources** \\  & **Coefficient** & **by C)** & **Data Sources** \\ \hline Production, transportation, & 0.8956 & kg/kg & ORNL (Oak Ridge National Laboratory, USA) \\ and use of fertilizers & 4.9341 & kg/kg & ORNL (Oak Ridge National Laboratory, USA) \\ Production, transportation, & 5.18 & kg/kg & IREEA (Institute of Agricultural Resources and Ecological Environment, Nanjing Agricultural University) \\ Agricultural machinery & 0.5927 & kg/kg & IPCC (United Nations Intergovernmental Committee of Experts on Climate Change) \\  & 266.48 & kg/hm\({}^{2}\) & [PERSON] et al. [33] \\ \hline \end{tabular}
\end{table} 
Table 2: Carbon emissions coefficients for agricultural inputs. \[\mathrm{O_{N2O}}=\mathrm{N_{O}}\times\mathrm{E_{N}}\times 298\]  
\[\mathrm{N_{O}}=\sum_{i=1}^{n}\frac{\mathrm{A_{i}}\times\mathrm{T_{i}}}{365} \times\mathrm{E_{i}}\times\mathrm{W_{i}}\]  
Among them, \(\mathrm{N_{O}}\) is the nitrogen input of organic fertilizer. It is based on the situation of returning the manure generated from livestock and poultry breeding to the field. Therefore, the accounting of the situation of returning the manure generated from livestock and poultry breeding to the field is shown in the second formula. \(\mathrm{A_{i}}\) represents the year-end inventory of the \(i\)_th_ type of livestock and poultry in Beijing (of which poultry is the annual slaughter volume). \(\mathrm{T_{i}}\) represents the growth cycle of the \(i\)_th_ type of livestock and poultry. \(\mathrm{E_{i}}\) represents the average annual nitrogen excretion coefficient of the \(i\)_th_ type of livestock and poultry manure. \(\mathrm{W_{i}}\) represents the return rate of the manure of the \(i\)_th_ type of livestock and poultry to the field.