| The rapid development of social economy and the continuous promotion of industrialization and urbanization have brought new technological revolution and great opportunities for agricultural production,but also increased new demands and challenges.Jianghan Plain is located in the Middle-South of Hubei Province.It is one of the commodity grain bases in China.There are large fertile fields in the territory,which plays an important role in the grain production and food security of Hubei Province and the country.Although the grain production in this region has been maintaining a high level of output,there are also some phenomena that can not be ignored in recent years.As the urbanization process is accelerating,more and more rural laborers are flowing into the city.At the same time,the economic benefits brought by grain production are relatively low,and the enthusiasm of farmers to agricultural production is gradually reduced,which makes the arable land in many areas of Jianghan Plain abandoned and idle.In addition,the prevalence of crayfish-rice culture in Jianghan Plain in recent years also led to the change of a large number of cultivated land into crayfish-rice fields.Affected by the economic benefits of crayfish,the enthusiasm of overwintering crops cultivation in crayfish-rice fields is not high,which further increases the expansion of the area of crayfish-rice fallow fields.In view of the continuous expansion of winter fallow fields in Jianghan Plain and the continuous reduction of winter crop planting area,this paper uses Landsat 5/7,HJ-1A/B,Sentinel-2 and other remote sensing data to extract the winter crop distribution in Jianghan Plain from 2000 to 2020,and further extracts the distribution range of winter fallow fields by using 30m spatial resolution Globe Land30 land cover/use dataset.In order to provide scientific monitoring data and theoretical support for agricultural production and cultivated land utilization in Jianghan Plain,the spatio-temporal distribution characteristics of winter fallow fields and the driving factors affecting the expansion of winter fallow fields were discussed.The main results are as follows:(1)Using multi-source remote sensing data and existing land cover/use dataset can not only accurately extract the distribution of winter crops and winter fallow fields in large areas,but also the extraction method is simple and fast.The overall accuracy of the extraction results is between 85.29%and 88.87%,and the Kappa coefficient is above 0.77,which meets the accuracy requirements of large area winter fallow field monitoring.(2)The area of winter fallow fields in Jianghan Plain in 2000,2005,2010,2015 and 2020were extracted and calculated by the above method,and the results were 14596.3km~2,16438.5km~2,15588.5km~2,17311.9km~2 and 21362.1km~2 respectively.On the whole,except for a small fluctuation in the middle,the area of winter fallow farmland in Jianghan Plain has increased by 6765.8 km~2 from 2000 to 2020,an increase of 46.35%on the basis of 2000.(3)From the spatial point of view,the spatial characteristics of winter fallow fields and winter crops in Jianghan Plain are also obvious.Among them,winter crops are mainly distributed in two zones:first,the area on both sides of the Hanjiang River where"Xiantao West–Tianmen–Zhongxiang-Yicheng"is located.Second,the area on both sides of the Yangtze River where“Shishou–Jiangling-Gongan-Jingzhou District-Songzi East-Zhijiang”is located.The winter fallow field is widely distributed,mainly showing three parallel strips,and the direction is"northwest to Southeast",specifically as follows:the first strip,from the north of Yicheng to Caidian.The second belt is from Shayang to Honghu;the third belt is from the west of Zhijiang to the south of Shishou.Winter fallow fields are mainly distributed in paddy soil types(2020:61.88%),and the proportion of winter fallow fields in fluvo-aquic soil types is only 25.98%(2020).Based on the calculation results of the ratio of winter fallow fields to winter crop areas of various soil types,the ratio of paddy soil is 4.08 in 2020,which is about2.5 times of that of fluvo-aquic soil types,indicating that winter fallow fields expand significantly in the rice planting area of Jianghan Plain.(4)Through Pearson correlation analysis,it was found that there was a strong positive correlation between the area of water bearing winter fallow field in spring 2020 and the annual output of crayfish in 2019 in Jianghan Plain,and the correlation coefficient was as high as 0.902.At the same time,the correlation coefficient between the area of winter fallow fields and the number of migrant population in each county(city,region)is increasing in 2010,2015 and 2020,and the trend-line slope k value of scatter plot fitting is also increasing.Comprehensive analysis shows that the expansion of crayfish-rice fields and the increase of migrant population have promoted the expansion of winter fallow fields in Jianghan Plain.Meanwhile,the impact of migrant population on the expansion of winter fallow fields has been deepening in recent ten years.(5)After detecting the driving factors that may affect the expansion of winter fallow fields in Jianghan Plain from 2000 to 2020 by Geodetector,it is found that the q value of altitude,slope,per capita GDP,distance from Hanjiang River of Yangtze River and other factors pass the P value 0.01 significance test,but the influence degree of single factor is relatively small.However,the q value of interactive detection of altitude,slope and per capita GDP with other factors has been significantly improved,and most of them show nonlinear effects among multiple factors.The results show that terrain factors(elevation,slope)and per capita GDP factors play a certain driving role in the expansion and change of winter fallow fields in Jianghan Plain,which makes the agricultural winter crop planting area continue to shrink. |
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