| The development and utilization of cultivated land ecosystem,which has led to an main form of cultivated land use change,i.e.,crop planting structure change,was widely implemented by human beings to obtain the direct and indirect benefits for their own survival and development.As an intuitive expression of the human use actuality of agricultural resources,the information of crop planting structure concerning type,quantity,percentage and spatial distribution of crop is a significant data source for the researches on crop production balance,the optimizing management of agricultural production and the rational adjustment of crop planting.On the premise of the timely and accurate acquisition of crop planting structure,a penetrating understanding as regards the characteristics and driving factors of crop planting structure changes will play a significant role in solving the increasingly prominent contradiction between human and land,achieving the regional sustainable development and safeguarding national food security.In view of these,the Heihe River Basin in the arid and semi-arid area of northwest China was selected as the study area of my research,and Thematic Mapper,Enhanced Thematic Mapper Plus and Operational Land Imager(TM/ETM+/OLI)remote sensing images were selected as the data source according to the spatial scale and time scale of this research,as well as the characteristics of the Heihe River Basin with fragmented cultivated land and a complex crop planting structure.Subsequently,an elaborate classification was performed to extract crop planting structure of the Heihe River Basin in 2007,2012 and 2014 based on TM/ETM+/OLI images and the data of crop phenophase using the methods of multi-temporal NDVI,time window threshold value and decision tree algorithm.In addition,the spatial and temporal changes of crop planting structure were analyzed to reveal the characteristics and driving factors of these changes.Moreover,from the perspective of crop planting structure changes,the ecosystem services value of each crop was evaluated based on market value method,and the effects of crop planting structure changes on ecosystem services value of cultivated land was analyzed.The main conclusions of my research were as follows:(i)TM/ETM+/OLI images with high spatial resolution and appropriate temporal resolution are suitable data source for a large spatial scale and long time scale extraction of crop planting structure in the areas with fragmented cultivated land and a complexcrop planting structure.The overall accuracy of crop planting structure extraction in the Heihe River Basin in 2012 was 85.51%.(ii)From 2007 to 2014,the most widely-spread crop corn was mainly distributed in Ganzhou District,Linze County,Gaotai County,Suzhou District and Jinta County,and wheat,barley and rapeseed were mainly distributed in Minle County and Shandan County in the Heihe River Basin.The planting area and proportion of corn and rapeseed increased,while those of wheat and barley decreased.Inaddition,the planting of corn showed a concentration trend,and wheat,barley and rapeseed showed a trend of scattered planting.The dominance degree of cron planting was higher than that of wheat,barley and rapeseed and continuously showed a trend of increase.The fragmentation and diversity of crop distribution in cultivated land landscape increased due to the intervention of human productive activities.(iii)The changes of crop planting structure in the Heihe River Basin were the results of the more rational planting choices of farmers about crop type,and these rational choices were mutually influenced by the factors of socioeconomic,policy,natural conditions and other aspects.Under the precondition of suitable natural conditions,generally,farmers preferred planting cash crop,which has higher economic benefits.(iv)The changes of crop planting structure in the Heihe River Basin,the increasing planting area and proportion of corn and rapeseed and the decreasing planting area and proportion of of wheat and barley,will facilitate to not only improve the economic benefits of crop planting and alleviate the temporal contradiction of agricultural irrigation water,but also improve the ecosystem services value of cultivated land and maintain sustainable development in the Heihe River Basin. |
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