**5. Conclusions**

Based on 1 km land-use grid data from 1990 to 2020, this study applied a landscape analysis, the land-use change matrix for different topographic grades of China, to determine the divergent patterns and the spatial–temporal changes in paddy field and dryland resources under different terrain gradients. The results show that:

First, although paddy field and dryland were mostly distributed in areas with better photothermal conditions, the area of paddy fields and drylands on sunny slopes significantly decreased in recent years. The area of paddy fields and drylands on the southeastern, southern, and southwestern slopes decreased, while the area of paddy fields and drylands on the northwestern, northern, and northeast slopes increased.

Second, from 1990 to 2020, land conversion between paddy field, dryland, and other land was mainly concentrated in the third ladder (0–200 m DEM), but the changes in the second ladder (500–2500 m DEM) became prominent.

Third, paddy field and dryland went "up the hill". Paddy field and dryland at lowelevation, low-sloping areas were reduced, and those at higher-elevation, higher-sloping areas increased, which may trigger potential soil erosion. Meanwhile, at high slopes and high elevations, the transition from paddy field to dryland was more prominent.

Finally, there were differences in the landscape characteristics of paddy field and dryland. Although the fragmentation of patches, dispersion of distribution, and complexity of shapes of paddy field landscapes increased, the new paddy field showed the characteristics of aggregation in some areas (such as the northeast and Sichuan). In contrast, although the fragmentation of patches, dispersion of distribution, and complexity of shapes of dryland landscapes increased, the landscape agglomeration characteristics were higher compared to paddy field, decreasing with time.

Based on the research findings, this paper puts forward some suggestions on the utilization of paddy field and dryland. Firstly, the government should strengthen the protection of arable land on sunny slopes and control the conversion from arable land to construction land on sunny slopes in traditional agricultural production areas. Secondly, the protection of water resources in the utilization of arable land in the second ladder regions (such as Xinjiang and Gansu) should be strengthened, and unsuitable arable land should be retired from agricultural production. Thirdly, the government should protect the arable land on the plain area and limit the extensive use of paddy field and dryland on sloping areas to reduce the aggravation of soil erosion. Lastly, land consolidation should emphasize reducing the landscape fragmentation and dispersed distribution of arable land patches.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/land11101851/s1. Table S1: The area of paddy field and dryland under different TPI in China in 1990 and 2020; Table S2: Change in the elevations of paddy field and dryland; Table S3: Change in the slopes of paddy field and dryland; Table S4: Change in slope aspects of paddy field and dryland; Table S5: Land use transformation matrices for paddy field, dryland, and other land among the 32 provinces; Table S6: Landscape indices of paddy field in different elevations; Table S7: Landscape indices of paddy field in different slopes; Table S8: Landscape indices of paddy field in different slope aspects; Table S9: Landscape indices of dryland in different elevations; Table S10: Landscape indices of dryland in different slopes; Table S11: Landscape indices of dryland in different slope aspects.

**Author Contributions:** Conceptualization, S.X.; methodology, S.X.; software, S.X.; formal analysis, S.X.; investigation, W.W., Q.S. and Z.Z.; data curation, S.X. and W.W.; writing—original draft preparation, S.X.; writing—review and editing, G.Y.; visualization, S.X.; supervision, G.Y.; project administration, S.X.; funding acquisition, G.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This paper was funded by the National Natural Science Foundation of China (Project No. 42171253); the Humanities and Social Sciences Foundation of Shandong Province, China (Project No. 2021-JCGL-08); the Shandong Social Science Planning Fund Program (Project No. 21CCXJ15); the Youth Innovation Team of Shandong Universities, China–"The Youth Innovation Science and Technology Support Program" (Project No. 2021RW034); the Research Project of Teaching Reform of Shandong Normal University (2019XM42).

**Data Availability Statement:** Data are available in a publicly accessible repository that does not issue DOIs. Publicly available data sets were analyzed in this study. These data can be found here: https://www.resdc.cn/, accessed on 10 February 2021.

**Acknowledgments:** The authors extend great gratitude to the anonymous reviewers and editors for their helpful review and critical comments. We confirm all individuals consent.

**Conflicts of Interest:** The authors declare no conflict of interest.
