| According to the estimates of FAO,more than one-eighth of the global population engages in agricultural activities in urban and peri-urban areas.Urban and peri-urban agriculture plays a significant role in ensuring food supply,supporting livelihoods,and providing ecological services in the city regions.Within the framework of urban-rural integrated development in China,peri-urban agriculture(PUA)has become a frontier industry,bridging the two national strategies of new urbanization and rural revitalization.Cropland as the core element,is facing various challenges related to degradation at the urban-rural interface,which limits the development of PUA.Amidst ongoing urbanization pressure,peri-urban cropland faces more degradation issues than traditional agricultural regions,such as land fragmentation,soil pollution,and declining fertility.Additionally,the mixed land use environment in peri-urban areas also triggers a range of degradation risks for cropland in peri-urban areas,and it is urgent to clarify the underlying mechanisms.Therefore,there is a need to explore strategies for conserving and improving peri-urban cropland,thereby facilitating the sustainable development of PUA.The peri-urban areas of Changchun City,located in the typical Mollisol region of Northeast China,were selected as the study area.A multidimensional cropland quality assessment system,which included soil fertility(SF),land fragmentation(LF),soil contamination(SC),and ecological quality(EQ),was established.The spatial variation characteristics of multiple cropland quality and their trade-off and synergy relationship were compared,thus providing a basis for guiding the systematic conservation of peri-urban cropland.The study also identified the significant factors that influence cropland quality,and explored their interactive effects in relation to agriculture,nature,urbanization,and policy,using the geographical detector.The gradient boosting decision tree(GBDT)algorithm was applied to quantify the nonlinear influence of significant factors and their relative importance in space.This contributes to guiding the rational utilization of peri-urban cropland.Finally,a comprehensive zone for land utilizing and conserving was developed based on the spatial variation pattern and its degradation mechanism of cropland quality,within the existing basic farmland protection zones.The results aimed to contribute to the development of differentiated protection policies for peri-urban cropland,and promote the transformation of PUA in the context of rapid urbanization in the Mollisol region of Northeast China.The main research conclusions were as follows:(1)Spatial heterogeneity was observed in all dimensions of cropland quality.Addressing the degradation issues with one-size-fits-all measures of quality improvement was difficult.The spatial autocorrelation of SF and SC in the study area was high.Cropland with low SF was predominantly distributed around the Changchun-Gongzhuling coordinated development axis,while the distribution of high-risk SC were coincidentally associated with the industrial parks planned in the western industrial corridor of Changchun.Moderate spatial autocorrelation was observed in LF and EQ.The suburban belt exhibited concentrated cold-spots of LF.Cold-spots of EQ were dispersed around the main urban areas and satellite towns.On the transition gradient from urban to rural areas,both the LF and EQ exhibited an upward trend,and they were inferior near the urban area.The SF also exhibited an increasing urban-rural transition trend within a 10 km radius from the urban area,but gradually decreased beyond this distance.The distribution of EQ near the urban area was dispersed,but it gradually converged and stabilized at middle level as the distance from the urban area increased.(2)Taking into account the complex trade-offs and synergistic relationships that exist amidst the spatial heterogeneity of cropland quality is crucial when implementing measures to enhance its quality.In the middle section(7-17 km)of the urban-rural transition,the relationship between SF and LF demonstrated significant synergy.Land consolidation of fragmented cropland could enhance fertility maintenance by influencing farmers’decision-making processes.The trade-offs between SF and SC were mainly distributed far away from the urban area,where the application of fertilizers to enhance cropland yields would amplify the contamination risk.SC-LF and SC-EQ predominantly exhibited synergistic relationships within the study area,suggesting that enhancing cropland ecological services and site conditions could contribute to the improvement of environmental quality.The changes in the trade-off relationship concerning EQ and SF exhibited a similar pattern to that of synergy along the urban-rural gradient.This trend is equally observed in the relationship between EQ and LF.Therefore,quality management aimed at enhancing the production function of cropland should carefully consider spatial information to mitigate any adverse effects on other ecological functions.For systematic improvement of cropland quality,effective resolution of the challenges posed by the intertwined relationships of trade-offs and synergies can be achieved through the implementation of clustering and zoning approaches that consider the spatial similarity of various dimensions of cropland quality.(3)Urbanization played a dominant role among the various factors affecting the quality of peri-urban cropland,while agricultural and policy factors also contributed to altering its natural distribution pattern.The factor detection revealed that urbanization factors,such as population change and urbanization speed,accounted for 28.95%of the explanatory power for the spatial distribution of SF,while natural and agricultural factors followed closely.Urbanization was also the major factor in changing LF of peri-urban cropland,but the explanatory power of the basic farmland protection rate(a policy factor)was also high(q=0.21).Industrial density emerged as the primary determinant of the spatial distribution of SC,with an explanatory power of 26.46%as an urbanization factor.In addition,natural factors like topography and soil exerted a substantial influence on SC.EQ was primarily shaped by natural factors,although two urbanization factors,namely population change and industrial density,had altered its natural distribution pattern.Further interaction detection demonstrated that the explanatory power of the interactions between significant factors surpassed their individual explanatory power,signifying the interdependence of multiple factors in peri-urban areas in determining the spatial distribution of cropland quality.(4)Human activities,including urbanization and agricultural tillage,had a non-linear impact on cropland quality.By controlling land use intensity within proper threshold,the risks of cropland degradation could be avoided.The GBDT algorithm indicated that the agglomeration of industries at a density of 0.05-0.125/km~2 could be beneficial in mitigating the contamination threats.Pesticide inputs below 300 yuan/ha could also minimize their negative environmental effects,and relevant agricultural intensification was beneficial for SF conservation.Meanwhile,relatively slow urbanization speed could improve SF by maintaining stable expectations of returns on cropland investments.In terms of LF,controlling the density of road network(<3 km/km~2)and the cropland forest shelterbelt(<4 km/km~2)could effectively restrain its fragmentation trend.Crop residue cover reflected by NDTI only had positive effects on EQ within the threshold of 0-0.03 and 0.08-0.10.Therefore,it is necessary to scientifically determine the straw coverage rate based on the decomposition capacity of soil when promoting no-tillage technology.Additionally,the spatially weighted GBDT algorithm quantified the spatial impact intensity of significant factors.The results showed that the relative importance of urbanization factors was generally higher within a range of 6-8 km from the urban area,and the impact intensity gradually decreased beyond this distance threshold.(5)The cropland management policy within the basic farmland zoning was further refined through the logical integration of comprehensive cropland quality,multidimensional competition relationships,and potential degradation risk.Land conserving zones(i.e.,land treatment zone)and land utilizing zones(i.e.,disturbance sheltering zone,tillage improvement zone,and agricultural restructuring zone)were delineated to support the peri-urban cropland quality improvement.In terms of land conserving,the construction of high-standard cropland in traditional agricultural areas was also the primary approach to prevent the LF of peri-urban cropland.However,the quality conservation in other dimensions required further refinement and adjustment in peri-urban areas.The specific implementation of measures should be accurate and well-organized,considering the spatial distribution pattern of cropland quality.Integrating these measures according to the synergistic relationships between different dimensions of cropland quality was also important to avoid unnecessary duplication of financial investment.In terms of land utilizing,the zoning regulations for cropland should be consistent across various administrative regions to mitigate the risk of land degradation.Among these zones,the disturbance sheltering zone was specifically designed to mitigate threats posed by urbanization,with the key factor being the selection of the scale and type of ecological buffer.Cropland in agricultural restructuring zones should reduce its dependence on quality attributes by expanding its multifunctionality,such as tourism,recreation,and education.Successful implementation of the tillage improvement zone primarily relied on policy regulations and tax incentives. |
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