| Land,the most important natural resource of human life,carries production,life and ecological spaces for human beings.It is also a critical political resource,bearing the stability and development of a country.As a form of utilization,cultivated land is an important material for the survival of human beings.The protection of cultivated land plays key roles in guaranteeing national food security,maintaining social stability and promoting the sustainable development of economy and society.These are closely related to quantity and quality of cultivated land.China is a country with a huge amount of agricultural population.With the rapid economic development and population growth in China,decreasing quantity and quality of cultivated land resulted in increasingly acute contradiction between human and land.Fertility loss of cultivated land,secondary salinization,acid rain,heavy metals,soil erosion and other environmental issues of soil also threatened the health of cultivated land and affected crop yield and quality.The management objectives of quantity,quality and ecology of cultivated land should be achieved through scientific control of the health status of cultivated land.The comprehensive health assessment of cultivated land responds current social demands and presents scientific and academic values.The influential factors of cultivated land healthy status presented spatial heterogeneity in the literature.This study selected the Helingeer County,located in ecological fragile regions of Inner Mongolia,as case study to illustrate the health assessment indicator system for cultivated land.The methodology of this dissertation was based on remote sensing(RS)and geographic information systems(GIS)technologies,landscape pattern index,dynamic degree,spatial analysis model and spatial change rate index.The soil characteristics,landscape characteristics and topographic characteristics of cultivated land,as well as the changing characteristics and evolution factors of 20-year cultivated land functional areas were systematically investigated.The cultivated land health indicator system was developed and the cultivated land health was evaluated by Matter-element Extension model.By the analysis of Obstacle Degree model,the dissertation improved cultivated land management and sustainable utilization from the perspective of dominant limiting factors and health level zoning.The specific research results are as follows:(1)The result indicated that land use types mainly consist of cultivated land,forestland and grassland in the study area.The spatial pattern of cultivated land was obviously different with other land use types.The cultivated land mainly distributed in the northern plains and rolling loess region,but in mountainous-region was rare.The patches of cultivated land in the plain area were large and concentrated.But,in the loess region and mountainous region,patches of cultivated land were relatively fragmented,which resulted in unique ecological landscape pattern.(2)The historical analysis for Ecological-living-industrial land indicated the productive function space of cultivated land has gradually shifted to the northern plain area and banks of the river in the past 20 years.In addition,the ecological environment of cultivated land has gradually improved.Although areas of cultivated land for industrial and ecological functions were gradually decreasing,the amount of cultivated land has met the demand of residents in the county during the period.The increase of constructions occupied cultivated land and resulted in the reduction of high quality cultivated land.The new increased cultivated land was mainly from reclamation of undeveloped land for ecological conservation purpose,because of their fragile ecological environment and barren natural conditions.The balance of occupations and supplements for cultivated land only realized in the quantity of cultivated land,but the reduction of quality of cultivated land was not fully considered that caused worse contradiction between the increasing demand of cultivated land and the degradation of cultivated land.The natural factors,socio-economic factors,comparative interests and policy factors have influenced the evolution of cultivated land functional areas.(3)With the model builder of ArcGIS 10.3,assignment models for vector format and raster format thematic maps were conducted respectively.The fast,scientific and accurate assignment for evaluation unit and attribute database of evaluation unit were realized.(4)Based on natural conditions and the characteristics of land use in the study area,the health assessment system for cultivated land was developed with multiple targets for land quality,productivity and land environment.The quality indicators of cultivated land included effective accumulated temperature of 10℃,topography,slope,land texture,effective soil thickness,organic matter contents,total nitrogen,effective phosphorus,available potassium,irrigation guarantee rate and drainage conditions.The productivity indicators of cultivated land included standard crop yield and patch connectivity.The land environmental indicators of cultivated land included soil erosion degree,salinization degree,distance between home and cultivated land,transportation accessibility and influence of urban area.(5)AHP was used to determine the weights of evaluation factors.Matter-element extension model was used to evaluate the health level of cultivated land.The comprehensive evaluation made evaluation results quantitative,scientific and accurate.Evaluation results also presented the spatial differences of cultivated land health level in the study area.(6)The health levels of cultivated land in the study area were classified into healthy,sub-healthy and unhealthy level,and the very healthy cultivated land was missing.Healthy cultivated land accounted for 52.69%,and the overall health status was below the moderate level.Healthy cultivated land was distributed in towns of the northern plains and the Hun River,sub-healthy cultivated land was distributed in the loess hilly region and mountainous region,and unhealthy cultivated land was scattered in the southern and eastern mountainous areas.The content of organic matter,effective phosphorus and available potassium in the healthy cultivated land in the study area were lower than those in the sub-healthy cultivated land,but the total nitrogen was higher than the sub-healthy cultivated land.That meant the soil nutrients in the healthy cultivated land were lower than that in the sub-healthy cultivated land.However,natural conditions,ecological environment and social conditions restricted the sub-healthy cultivated land.The characteristics of cultivated land and the external environment also affected the health level of cultivated land.(7)The Obstacle Degree model was used to identify high,medium and low limitation classes for constraints in evaluation units.The first and second principle constraints in the high limitation class of cultivated land were used to delineate principle constraint zones for each health status.The principle constraint zones of healthy cultivated land included irrigation guarantee rate,organic matter and effective phosphorus indicators.The zone of organic matter had the largest area among three constraints,accounting for 91.73%of the healthy cultivated land.The principle constraint zones of sub-healthy cultivated land included transportation accessibility,soil erosion,slope,irrigation guarantee rate and effective soil thickness.The zones of effective soil thickness and soil erosion accounted for 63.71%of the sub-healthy cultivated land.The principle constraint zones of unhealthy cultivated land included soil erosion,slope and effective soil thickness,particularly,the effective soil thickness and soil erosion.(8)Based on the constraint factors of the dominant constraint zoning,the cultivated land health assessment improved cultivate land management and protection measures on evaluationing unit and provided suggestions for sustainable utilization of cultivated land.Provides a reference for future method research of health assessment of cultivated land.Moreover,it provides the reliable theoretical basis for delimiting prime farmland,building high standard farmland,processing land consolidation and formulating protection policy for cultivated land.The management and protection measures of healthy cultivated land will mainly focus on popularizing the technology of straw returning to field,implementing the system of fallow rotation,improving the basic facilities of cultivated land and comprehensive reforming prime farmland.The management and protection measures of sub-health cultivated land will mainly focus on saline-alkali land improvement,slope land improvement,rational application of chemical fertilizers to balance soil nutrients,increase the thickness of tillage layer and leveling cultivated land slope farmland,returning cultivated land to forests and grasslands,sealing slope and consolidating soil.The management and protection measures of unhealthy cultivated land will mainly focus on returning farmland to forest and pasture.In mountainous areas,where desertification and aeolian sandy soil are dominant,trees are suggested to be planted under better water conservancy conditions,and shrubs and forages are planted when topography becomes higher and sandy layer becomes thicker to prevent wind and fix sand.The mobile aeolian sandy soil will be fixed by step-by-step enclosure with grass-shrub method.Achieving the combination of tree-shrub-grass controls soil and water step by step. |
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