## 3 Results
### Spatiotemporal Changes of the CLQ
#### 3.2.2 Spatiotemporal Changes of CLQ in Unchanged/Lost/Gained Area  
Spatiotemporal changes of CLQ in the unchanged area (cultivated land that had not been converted to other land use types during the study period) are presented in Table 5. In these three different periods, the quality grade of about 50% of the cultivated land did not change. The proportion of cultivated land with an improved quality grade (including improvement by 2 grades and 1 grade) was greater than that of the cultivated land with a decreased quality grade (including a decrease by 2 grades and 1 grade). This indicated that the quality of the unchanged cultivated land improved from 2010 to 2018. Spatially, the unchanged cultivated land with no change in quality grade was widely distributed throughout the entire study area. The unchanged cultivated land with improved quality (including improvement by 2 grades and 1 grade) was mainly concentrated in the eastern, northern, and southern parts of Guangzhou. The unchanged cultivated land with decreased quality (including a decrease by 2 grades and 1 grade) was mainly concentrated in the western part of Guangzhou (Figure 6). Figure 5: Spatial distribution of the cultivated land quality (CLQ) grade in Guangzhou: (**a**) 2010; (**b**) 2015; (**c**) 2018. Spatiotemporal changes of CLQ in lost/gained area (including the lost cultivated land in the previous year and the gained cultivated land in the following year during the study periods) are presented in Table 6. In these three different periods, the lost cultivated land (cultivated land converted to non-cultivated land) was mainly medium quality and low quality, accounting for about 77%, while the gained cultivated land (non-cultivated land converted to cultivated land) was mainly high quality and medium quality, accounting for about 72%. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & **Statistical Measure** & **Improved by 2 Grades** & **Improved by 1 Grade** & **Grade** & **Decreased by 1 Grade** & **Decreased by 2 Grades** \\ \hline \multirow{2}{*}{2010–2015} & Area (ha) & 2438 & 15,772 & 35,051 & 15,683 & 1873 \\  & Percent (\%) & 3.44 & 22.27 & 49.49 & 22.15 & 2.65 \\  & Area (ha) & 3265 & 19,131 & 37,156 & 13,069 & 1143 \\  & Percent (\%) & 4.43 & 25.93 & 50.37 & 17.72 & 1.55 \\  & Area (ha) & 3949 & 17,685 & 29,998 & 11,192 & 1531 \\  & Percent (\%) & 6.14 & 27.48 & 46.61 & 17.39 & 2.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Change characteristics of CLQ in unchanged area. Figure 6: Spatial characteristics of the quality change of the unchanged cultivated land in the different study periods: (**a**) 2010–2015; (**b**) 2015–2018; (**c**) 2010–2018. There was large spatial heterogeneity in the quality changes of the lost/gained cultivated land. From 2010 to 2015 and from 2010 to 2018, the lost medium-quality and low-quality cultivated lands were mainly located in the southern and western parts of Guangzhou. The gained medium- and high-quality cultivated lands were mainly concentrated in the eastern and central-northern areas (Figure 7a,c). From 2015 to 2018, the lost medium- and low-quality cultivated lands were mainly located in the western and northern parts of Guangzhou. The gained medium- and high-quality cultivated lands were mainly concentrated in the eastern and southern areas (Figure 7b).