## 3 Results and Analysis
### Relative Contributions of Agricultural Inputs to the TCF  
The relative contributions of carbon footprints induced by 10 main agricultural inputs to the TCF for four periods are displayed in Figure 4. Based on the values of relative contributions for various agricultural inputs from 1995 to 2016, the contributors could be divided into three groups, i.e., higher contributors, including nitrogen (48.54%), electricity (13.65%), and diesel (12.36%); moderate contributors, including raw coal (9.23%), gasoline (5.78%) and pesticides (4.99%); and lower contributors, including plastic film (2.56%), phosphorus (2.09%), and potassium (0.80%). The relative contributions indicated that 92.46% of the TCF was contributed by chemical fertilizers and energy consumption; while only 7.54% of the total CF was contributed by pesticides and plastic film use (Figure 4). The CF caused by nitrogen input induced N\({}_{2}\)O was even greater than that caused by electricity use. The CF caused by energy consumption was 41.02% of the TCF. Particularly, the relative contribution of CF caused by electricity use roughly decreased from 1995 to 2011; however, it rapidly increased after 2011.  
The CF caused by plastic film was only 2.56% of the TCF; yet, it had a higher rate of increase than those caused by other agrochemical inputs over 1995-2016. The relative CF caused by plastic film in the study area increased even faster than that in China. The CF caused by diesel was 12.36% of the TCF, lower than that by electricity; yet, it had a higher rate of increase than those caused by other agricultural energy inputs over 1995-2016. The relative CF caused by diesel in the study area also increased faster than that in China (Figure 5).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & **Mean TCF** & **TCF Growth** & **Mean AV** & **AV Growth** & **Relative** & **Relative** \\  & **(Kt CE)** & **Rate (\%)** & **(BCNY *)** & **Rate (\%)** & **Contribution** & **Contribution** \\ \hline
1995–1999 & 196.92 & 1.57 & 5.89 & 2.61 & 49.57 & 42.36 \\
2000–2007 & 184.19 & \(-\)1.02 & 7.82 & 11.94 & 51.89 & 37.78 \\
2008–2016 & 270.08 & 4.85 & 24.30 & 20.70 & 44.98 & 43.16 \\
1995–2016 & 222.22 & 2.83 & 14.12 & 24.32 & 48.54 & 41.02 \\ \hline \hline \end{tabular}  
* Note: 1 BCNY = 10\({}^{9}\) CNY (Chinese Yuan); 1 Kt = 10\({}^{3}\) t.  
\end{table}
Table 2: Mean TCF and mean agricultural output values for four periods.  
Figure 4: Relative carbon footprint (CF) contributions of 10 emission sources to the TCF.  
The relative CF contributions of 10 emission sources to the TCF for four time periods are shown in Table 2 and Figure 4. The changing trend of TCF was mainly controlled by that of carbon footprints induced by N fertilizer and energy inputs. The relative mean CF contribution of N fertilizer to the TCF increased from 49.57% during the period 1995-1999 to 51.89% during the period 2000-2007, then dropped to 44.98% during the period 2008-2016 (Table 2). The changing trend for relative mean CF contribution of agricultural energy to TCF was contrary to that of N fertilizer to the TCF. Therefore, higher proportion of N fertilizer input over 2000-2007 during GFGP and higher proportion of agricultural energy consumption over 2008-2016 after GFGP could be found in the study area. Compared with the whole country [3], the study area had a lower proportion of N fertilizer input and a higher proportion of agricultural energy consumption.