| Cultivated land,as an important natural resource,is the basis for ensuring national food security and maintaining economic and social stability.With the continuous growth of population and the rapid development of social economy,the quantity and quality of cultivated land in China continue to decline under the dual influence of construction occupying a large number of high quality cultivated land and the degradation of cultivated land.In order to ensure the national food security,the ecological security of cultivated land and the sustainable utilization of cultivated land,in the protection of cultivated land in the new period and under the new situation,we should not only pay attention to the control of cultivated land quantity,but also take the protection and promotion of cultivated land quality as the strategic support point of storing grain in the land and storing grain in the technology.Southwest Hubei mountain area is an important national ecological barrier construction area,Hubei Province important biodiversity conservation area and forest ecological protection area.The ecological environment of this region is good and rich in resources.It is an ecological barrier in the middle and east of China.It is of great significance for soil and water conservation,water conservation and biodiversity conservation in Wuling Mountain area of the three Gorges Reservoir area.Under the influence of regional natural and social economic factors,there are many problems in the utilization of cultivated land in the mountainous area of southwest Hubei Province,such as frequent ecological problems of cultivated land,decline of cultivated land fertility,backward agricultural infrastructure and piecemeal land plots,which seriously affect the safety of cultivated land resources in this area.This paper takes Enshi Prefecture as a case study area in the southwest of Hubei Province to explore the temporal and spatial evolution law and influence mechanism of cultivated land resources since the second soil survey in the study area.The main contents of this paper are divided into 9 chapters:Chapter 1 is the introduction.The research background and significance are expounded.Firstly,the connotation of cultivated land and cultivated land quality is understood;the research progress of cultivated land quality evaluation at home and abroad is combed from the aspects of cultivated land quality evaluation index system,evaluation method,type,scale,space-time evolution,etc.The research progress of obstacle diagnosis is combed from the aspects of high standard farmland,cultivated land ecological security,cultivated land sustainable utilization,cultivated land quality obstacle,cultivated land multifunction and so on.On this basis,the objectives and contents of this study are determined,and the technical route,characteristics and innovations of this study are expounded.Chapter 2 is the theory and method.The theoretical basis of this paper is put forward,and the related research methods are introduced.Chapter 3 is the general situation and data source of the study area.The space-time scope of the study is defined,and the study area is introduced from the aspects of geographical location and administrative division,natural geographical profile,social and economic profile,and the data sources and preprocessing of this study are explained.Chapter 4 is the temporal and spatial evolution and influence mechanism of cultivated land utilization in southwest Hubei.Based on the statistical yearbook data and land use data of the study area since 1980,the present situation of cultivated land use is understood from the aspects of cultivated land spatial distribution characteristics,cultivated land resource characteristics,cultivated land pressure index and so on.The research shows that the total number of cultivated land in the study area has been decreasing since 1980,in which the decrease of cultivated land in 1980-2005 is small and the decrease in 2005-2018 is large.Returning farmland to forest is the main reason for the small area of cultivated land,followed by returning farmland to grass and construction occupation.From 1980 to 2018,the land conversion area of cultivated land in the study area is only 50.18%of the total area,which fully shows that the land conversion in the study area is more intense,and the intervention degree of human activities on the change of cultivated land use is stronger.The center of gravity of cultivated land shows the trend of migration from southeast to northwest.The degree of fragmentation of cultivated land decreased slightly,and the range of change was not large.Economic development,population growth,capital input and grain output,production efficiency and policy factors are the leading factors in the change of cultivated land quantity in Enshi Prefecture.The fifth chapter is the construction of cultivated land quality evaluation index system in southwest Hubei.Based on the existing research results,on the basis of discussing the temporal and spatial evolution of cultivated land use and its influence mechanism in the study area,the evaluation index system of cultivated land quality composed of 16 indexes was constructed.Chapter 6 is the temporal and spatial evolution and influence mechanism of cultivated land quality in southwest Hubei.The accuracy of the evaluation model is verified.On the basis of confirming the scientific and reasonable evaluation results of cultivated land quality,the quality of cultivated land in 1980,2005 and 2018 is evaluated,and the spatial distribution characteristics of cultivated land quality in three periods are expounded.The results show that the quality of cultivated land in the study area is improving from 1980 to 2018,in which the increase of higher-land area is slow,the increase is small,the increase of medium land area is faster and the increase is large,while the lower land area is gradually reduced.In stages,the quality of cultivated land improved slowly from 1980 to 2005 and faster from 2005 to 2018.From 1980 to 2018,the average grade of cultivated land in Enshi was 4.5 in 2018,and the quality of cultivated land was the best.Secondly,Xianfeng County,Hefeng County and Xuanen County,cultivated land quality grade between 5.27-5.34,after nearly 40 years of cultivated land quality protection and improvement,cultivated land quality improvement effect is obvious.However,the cultivated land quality in Laifeng County,Badong County,Jianshi County and Lichuan City is relatively low.The next stage is the core area of cultivated land quality improvement in the study area,which needs to increase investment and focus on management.the influence factors,such as topography,climate,cultivated land spatial form and so on,which are difficult to regulate,have little influence on the temporal and spatial evolution of cultivated land quality,while the human factors such as land use structure change,agricultural infrastructure perfection,fertilization,soil acidification,government policy and so on play a leading role in the spatial and temporal evolution of cultivated land quality in the study area.Chapter 7 is the temporal and spatial evolution and genetic analysis of cultivated land quality obstacle factors in southwest Hubei.With the help of the obstacle degree model,the factors of cultivated land quality obstacle in 1980,2005 and 2018 are analyzed as a whole,and the spatial distribution characteristics of cultivated land quality obstacle factors in three periods of each county and city are discussed.In the past 40 years,the temporal and spatial evolution and causes of different obstacle factors in counties and cities in the study area were further discussed,which provided the basis for confirming whether the obstacle factors of cultivated land quality in the study area were controllable and the size of the control space.Chapter 8 is the potential and strategy of cultivated land quality control in southwest Hubei.According to the temporal and spatial evolution characteristics and causes of cultivated land quality obstacle factors in the study area in the past 40 years,the controllability of cultivated land quality obstacle factors is determined.The spatial distribution characteristics of cultivated land quality obstacle types in the study area are analyzed,and the control measures are discussed.According to the research results,the factors that can regulate the quality of cultivated land are:thickness of tillage layer,soil bulk density,pH value,organic matter,available phosphorus,available potassium,slope of field surface,drainage capacity and irrigation capacity.The regulatory space is as follows:the thickness of tillage layer ≥ 30 cm,soil bulk density is 1.00-1.30 g/cm3,soil pH of 5.5-7.5 per cent,Soil organic matter content≥40 g/kg,Soil available potassium content≥200 mg/kg,The slope of the field is≤15°,Drainage capacity and irrigation capacity are up to and above the level.Ideally,the cultivated land quality control potential in the study area is 0.2628,Compared to the status quo,43.87 per cent;The optimal regulatory potential is 0.1861,Compared to the status quo,Up 31.07.The average grade of cultivated land quality in Enshi Prefecture is 1.06,Compared to the status quo,The average grade of cultivated land quality increased by 4.31;Under optimal conditions,the average grade of cultivated land quality in Enshi Prefecture is 2.87,Compared to the status quo,Up 2.50,The average grade difference between ideal condition and optimal condition is 1.81.The control potential under the optimal state can be used as an important reference basis for cultivated land quality control.There are three severe obstacles in the study area:slope limiting type,soil erosion type and irrigation limiting type,and strength obstacle 1:available potassium deficiency type.In terms of the distribution of counties and cities,there are 8 severe obstacles:slope limiting type,soil erosion type,irrigation limiting type,organic matter deficiency type,available potassium deficiency type,available phosphorus deficiency type,drainage restriction type,soil acidification type,intensity barrier 4:irrigation restricted type,soil acidification type,organic matter deficiency type,available potassium deficiency type.Finally,the spatial distribution characteristics and control measures of different types of cultivated land quality obstacles are analyzed and discussed.Chapter 9 is the conclusion and prospect.Summarize the main conclusions,point out the research deficiencies and research prospects. |
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