| Arable land is the basic condition for human survival.China feeds 20% of the world’s population with only 9% of the world’s arable land.In recent years,with the expansion of urban land and industrial land and continuous consumption of reserve arable land resources,the quantity and quality of arable land are threatened.Local practices such as occupying high-qualified arable land,supplementing poor-quality arable land,occupying the arable land on the plain,supplementing the arable land in hilly areas further cause serious unbalance between urban land use and rural land use.As the international food trade crisis caused by the COVID-19 appeared,the arable land use requires to be further optimized.To refine the research perspective more detail,this thesis subdivides the type of arable land into two secondary types: paddy field(it contains the land with irrigation facilities used to grow aquatic crops such as rice and lotus root)and dryland(it includes the land without irrigation facilities,the rain-fed land relied on natural precipitation,and the land with irrigation facilities).Based on 1 km*1 km land use grid data from 1990 to 2020,this study applied the land-use change matrix,Geo Detector analysis and so on to find the spatialtemporal changes,landscape characteristics,topographic differentiation,land class transformation and the driving mechanisms of paddy field and dry land resources in China,which can clarify the development direction of agricultural production and provide an important reference for the optimal use of arable land resources.The results show that:1)The difference of spatial and temporal patterns of paddy field and dryland reflects the recessive change of arable land use.From1990 to 2020,the paddy field decreased while the dryland increased,the loss of paddy field and dryland mostly occurred in the location with better natural endowments,but the new added paddy field and dryland concentrated in the areas with poor suitability.The change of the spatial distribution of paddy field and dryland was different among provinces.For example,the increase of paddy field in Heilongjiang,the increase of dryland in Xinjiang and the decrease of paddy field and dryland in Guangxi were significant.The transformation between paddy field and dryland was prominent,especially in Heilongjiang and Sichuan.The change of paddy field and dryland use presented a rapid-slow-rapid process with2000 and 2015 as turning points.The ratio between the grain crops area and cash crops area,the total water resources and the effective irrigation area were the main factors affecting the transformation between paddy field and dryland.In addition,the transformation from dryland to paddy field was affected by per capital arable land area and multiple cropping index,while the transformation from paddy field to dryland was affected by soil erosion and the annual sunshine duration.Compared with the transformation from dryland to paddy field,the change from paddy field to dryland was more sensitive to natural endowments.2)The topographic conditions of different arable land types have declined,and different arable land types showed great differences under different topographic gradients.From 1990 to2020,paddy field and dryland were mostly distributed in areas with better photothermal conditions.However,in recent years,the paddy field and dryland on the “sunny” slope decreased.Specifically,the area of paddy field and dryland on the southeast,south,and southwest slopes decreased,while increased on the northwest,north,and northeast slopes.From 1990 to 2020,the land conversions among paddy field,dryland,and other land use were mostly concentrated in the third ladder(0-500 m elevation)of China.However,the changes in paddy field,dryland and other land have become active on the second ladder of China(1000-2000 m elevation).Moreover,the change from other land to dryland on the second ladder accounted for nearly 50% of the country’s total change.Paddy fields and drylands reduced in areas with low elevation and low slopes and increased in those areas with higher elevation and higher slopes,indicated that the arable land in mountainous areas increased.These changes may aggravate soil erosion in the planting process.3)The landscape characteristics of both paddy field and dryland showed differentiation,and the paddy field and dryland landscape indices also varied greatly in different topographic gradients.Although the fragmentation,dispersion and shape complexity of paddy field landscapes increased,the new added paddy field landscapes showed agglomeration in local areas(such as Heilongjiang and Sichuan).In contrast,although the dryland was more aggregated,the shape was more complex,and the land plots were more fragmented,its landscape agglomeration characteristics were more pronounced compared to paddy field,and this characteristic has become weaker over time.4)From the perspective of recessive differences of arable land use,the utilization conditions of arable land should be improved according to local conditions,based on the regional resource endowment conditions and the change and distribution of the utilization of paddy field and dryland.It is necessary to deeply understand the differences of arable land resource endowments in China.In areas where have complex topography,poor water,fertilizer,air and heat conditions and serious soil erosion,it should focus on strengthening ecological protection,reducing the aggravation of soil erosion,and the coordination between arable land utilization and improving topography and the sustainability of paddy field and dryland utilization.The government should protect the arable land on the plain area and limit the extensive exploitation of paddy field and dryland on sloping areas.In special areas with active conversion between paddy field and dryland,it is necessary to adequately assess the suitability of this conversion.For the phenomenon of the conversion between paddy field and dryland due to uneven distribution of water resources,the construction of water source projects should be strengthened emphatically.The role of policy support such as land remediation and the construction of high-standard basic farmland should be fully utilized to improve the degree of concentration and infrastructure of paddy field and dryland,and to reduce the landscape fragmentation and dispersed distribution of arable land patches.And the government should strengthen the protection of arable land on sunny slopes and control the conversion from arable land on sunny slopes to construction land in traditional agricultural production areas.At the same time,the attention of the conversion among paddy field,dryland and other land should be strengthened,and unsuitable arable land should be retired from agricultural production.In the context of the dual game between the protection of arable land resources and the development of high-quality economy,it is of great practical significance to thoroughly discuss the internal structural problems of arable land in order to guarantee food security and enhance arable land utilization.Through relevant models,this thesis deeply observes the differentiation of different arable land types in terms of the spatial and temporal patterns,topographic conditions and landscape characteristics,and further refines the targeted optimization strategies for arable land utilization in different agricultural areas,so as to realize the optimization of arable land utilization and enhance land resource allocation efficiency from a refined perspective. |
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