| Food is an important basic resource related to China's development and strategic reserve,and food security is the top priority in national security.As a country with a large population,the food problem has a direct impact on China's long-term stability,and has become the focus of scholars at home and abroad.It is an important task to grasp the spatial and temporal change pattern of cultivated land and formulate corresponding policies and plans scientifically.Based on Landsat TM/OLI images in 2000 and 2017,this paper extracted the cultivated land information of Qian'an city by using object-oriented classification method,and based on this,explored the spatial and temporal pattern of cultivated land in Qian'an city and its ecological benefits,so as to provide scientific basis for relevant departments to formulate plans and policies.Monitoring the long-term changes in time and space of cultivated land in Qian'an city is of great significance for maintaining food security and agricultural development and sustainable development.The main conclusions of this study are as follows:(1)The object-oriented classification method was used to classify remote sensing images of Qian'an city and extract the cultivated land information of Qian'an city.366 verification points were used to evaluate the accuracy of the classification results.The results showed that the accuracy of cultivated land was 90.74%,the overall accuracy of the classification was 86.34%,and the Kappa coefficient was0.8292.The classification accuracy was high and could meet the requirements of this study.(2)In 2017,the cultivated land area of Qian'an city was 733.9 km~2,mainly distributed in the elevation of 50-100 m.In the past 17 years,the cultivated land of Qian'an city decreased by 45.56 km~2,and the area of Qian'an town decreased the most by 21.2 km~2.Most of the decrease in cultivated land went to artificial surfaces,which decreased by 119.4 km~2.(3)From 2000 to 2017,there was a significant difference in the change amount of cultivated land between towns in Qian'an.There were 7 towns with more cultivated land,There were 12 towns with increased cultivated land,Qian'an town was the fastest reducing town.In 17a,there were 5 towns with a cultivated land dynamic attitude of 0.5 or more,among which only the cultivated land of Pengdian town showed an increasing trend.From the perspective of the relative change rate,the relative change rate of cultivated land in each town of Qian'an city shows that the cultivated land development in Qian'an city was unbalanced from 2000 to 2017.The change rate of cultivated land in most towns of Qian'an was higher than the average change rate of cultivated land in the city.(4)between 17a,the center of gravity of Qian'an city shifted972.62m to the northeast,with an offset speed of 57.21m/a.The main reasons for the serious loss of cultivated land in southwest and the rapid expansion of cultivated land in northeast of Qian'an city.(5)in 2000 and 2017,the calculation of farmland landscape pattern,Qian'an concentration of cultivated lands is reduced,the fragmentation degree increase,connectivity,interference by human activities.(6)among many human driving factors,policy factors play an important guiding role;Population increase,economic growth and industrial restructuring,promote the rapid occupation of farmland.The increase of the input of science and technology in Qian'an city promotes the increase of the output of cultivated land per unit area and alleviates the impact of the decrease of cultivated land on food security to some extent.Figure 14;Table 15;Reference 61. |
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