# Agricultural Evolution: Process, Pattern and Water Resource Effect
## 3 Results
### Land Use Changes Related to Cultivated Land  
#### 3.2.1 Change Trajectory  
In our study, the initials of different land use categories were adopted to stand for different types to better illustrate cultivated land trajectories. For instance, \"F\" and \"G\" were applied to take the place of \"forest\" and \"grassland\", respectively. For dry farmland, the percentage of unchanged dry farmland is the largest. In detail, \"DDDD\", namely \"Dry farmland-Dry farmland-Dry farmland-Dry farmland\", occupied the largest percentage of land-use changes related to dry farmland changes (74.46%), following by \"GDDD\" (9.02%), namely \"Grassland-Dry farmland-Dry farmland-Dry farmland\", and \"UDDD\" (1.95%), namely \"Other unused land-Dry farmland-Dry farmland-Dry farmland\". For paddy field (Table 6), \"PPPP\", namely \"Paddy-Paddy-Paddy-Paddy\", occupied the largest percentage of land use changes related to paddy changes (30.32%), followed by \"2111\" (9.39%), namely \"Dry farmland-Paddy-Paddy\", and \"MPPP\" (7.17%), namely \"Marsh-Paddy-Paddy-Paddy\". Trajectory changes are classified as four types according to their steps, namely, unchanged, one-step, two-step and three-step changes. One-step changes accounted for the largest percentage \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type** & **Unchanged** & **One-Step** & **Two-Step** & **Three-Step** \\ \hline Paddy & 30.32\% & 51.87\% & 17.07\% & 0.14\% \\ Dry farmland & 74.46\% & 22.26\% & 2.58\% & 0.25\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Proportion of different kinds of change trajectories ( paddy and dry farmland). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type** & **Time** & **Longitude (E)** & **Latitude (N)** \\ \hline \multirow{4}{*}{Paddy} & 1990 & 124.01 & 45.97 \\  & 2000 & 123.96 & 45.9 \\  & 2010 & 123.97 & 46.02 \\  & 2015 & 123.88 & 46.11 \\ \hline \multirow{4}{*}{Dry farmland} & 1990 & 123.81 & 45.61 \\  & 2000 & 123.75 & 45.61 \\ \cline{1-1}  & 2010 & 123.74 & 45.62 \\ \cline{1-1}  & 2015 & 123.75 & 45.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Historical changes in gravity centers location. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type** & **Time** & **Distance (km)** & **Speed (km/a)** \\ \hline \multirow{3}{*}{Paddy} & 1990\(-\)2000 & 8.69 & 0.87 \\  & 2000\(-\)2010 & 13.37 & 1.34 \\  & 2010\(-\)2015 & 12.18 & 2.44 \\ \hline \multirow{3}{*}{Dry farmland} & 1990\(-\)2000 & 1.56 & 0.16 \\  & 2000\(-\)2010 & 4.04 & 0.40 \\ \cline{1-1}  & 2010\(-\)2015 & 2.36 & 0.47 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Historical changes in migration distance and speed of gravity center. (51.87%), followed by unchanged types (30.32%) and two-step changes (17.07%). Twenty-seven categories were contained in the one-step change types, including the conversion from marsh, dry farmland and grassland to paddy field (Table S1 in the Supplementary Materials). In addition, the transformation from unused land to paddy field also accounted for certain percentage such as \"UPPP\" (Unused land-Paddy-Paddy-Paddy) and \"UUPP\" (Unused land-Unused land-Paddy-Paddy). The transformation from unused land to paddy mostly indicated the conversion from saline-alkali land to paddy. Fifty-four categories and nine categories were included in two-step and three-step changes, respectively. For instance, the two-step change \"GDDP\" (Grassland-Dry farmland-Dry farmland-Paddy) means the transformation from grassland to dry farmland, and then from dry farmland to paddy field. Unchanged types accounted for the largest percentage (74.46%), followed by one-step types (22.26%) and two-step changes (2.58%). The percentage of unchanged types of dry farmland (74.46%) was much larger than that of paddy field (30.32%) while percentage of one-step changes of dry farmland was much smaller than that of paddy field (Table 6). Paddy fields need more water resources to survive their life than dry farmland. Therefore, dry farmland is usually more stable than paddy field.