A Study On Varied Cultivated Land Quality Using Site Conditions And Soil Geo-chemistry Characteristics As Indicators In A Peri-urban Area Of The Black Soil Region

Urbanization-induced non-agriculturalization of cultivated land resources is one primary phenomenon driven by the intense competition for land space between urban development and agricultural production.The ever-increasing urbanized land use not only occupies the quantity of cultivated land but also affects the cultivated land quality(CLQ)by reshaping the internal characteristics and the external utilizing conditions of cultivated lands.Moreover,the underlying variations are developed to be a hindrance for cultivated land use and efficient allocation of land resources in a peri-urban area.Therefore,it is of great significance to measure the degradation of peri-urban CLQ under the impacts of land urbanization as well as to adjust peri-urban land use appropriately and timely in terms of the regional CLQ and the utilizing conditions.As such,this research selected Kuancheng District in Changchun as a typical peri-urban area located in the black soil region to analyze the degradation of CLQ under the impacts of land urbanization by using site conditions and soil geochemical characteristics as indicators.Following the regional land use evolution and basic natural quality of cultivated land,we further measured the variations of peri-urban CLQ and its driving forces by using spatial analysis.We then concluded the distribution relationships between resources stability and utilization risks of peri-urban cultivated lands by using spatial mining method,and discussed the pressure they put on the peri-urban culitivated land use in the black soil region.The thesis aims to contribute to the protection of cultivated land resources and the development of peri-urban agriculture in the black soil area.The results were as follow,(1)The direct occupied area of cultivated land resources by urbanization during 2004-2014 was 4046.74 ha,which accounted for 26.82% of the total.The scale of land urbanization continued to increase,whereas there were vacant lands to be developed.In addition,the natural quality assessment of cultivated land indicated that the principal variations of classification indicators during 2004-2014 were the local soil acidification and reduction of soil organic matter,and the rest were relatively stable.The study area was mainly distributed with level-IV cultivated land(66.33%)in 2004,however,the proportion of level-IV cultivated land increased to 68.6% in 2014,and the level-V increased to 10.21%.The natural quality of cultivated land showed a downward trend in assessment levels overall under the impacts of land urbanization.(2)The site assessment proposed in this research was based on the LESA(Agricultural Land Evaluation and Site Assessment)system along with the original land use classification.Shape index(SI),area index(AI),contiguity index(CI),transportation convenience(TC),irrigation guarantee(IG),farming distance(FD),urbanization risk(UR)and ecological environment(EE)were selected to model the site condition for the cultivated land patch in a peri-urban area.The assessment results indicated that the levels of site condition mostly showed a downward trend during the urbanization process from 2004 to 2014.There was a large area of cultivated land with better site conditions being occupied for construction purposes,nevertheless,the site conditions of added cultivated land were barely satisfactory.Moreover,there was more than 25% of the total unconverted cultivated area in each period that was with decreased site condition levels,and a maldistribution could be detected.(3)The geochemical characteristics of cultivated top-soil varied prominently under the impacts of urbanization during 2004-2014.The variation was characterized by decreased concentrations of soil N,P,Ca,Se and S in the most urbanized area as well as elevated concentrations of soil Cr and Ni located near the industry development zone.Other than that,the results of spatial auto-regression showed that the land use and its spatiotemporal change formed another crucial impact factor that had influences on the variations besides natural background and agricultural activities.The urbanization-induced soil nutrient loss and heavy metal pollution were the geochemical factors that imposed restrictions on the peri-urban cultivated land use.(4)The area with decreased natural quality level,decreased site condition level,decreased soil nutrient assessment level and decreased soil heavy metal pollution assessment level were 3388.69 ha,4035.58 ha,365.19 ha and 233.63 ha,respectively,accounting for 83.74%,99.72%,9.02% and 5.77% of the direct occupied area.The statistics indicated that the influences on cultivated land resources caused by degradation of CLQ should be reckoned with.On the other hand,by using Logisitic-CA with restrained conditions,the area of cultivated lands that was potentially being occupied in five years or ten years by urbanization was forecasted to be 1632.88 ha and 3611.99 ha,respectively.The stability of cultivated land resources in a peri-urban area continued to decrease.Furthermore,the results of Apriori algorithm analysis indicated that the cultivated lands with decreased stability were mostly accompanied with the risk of decline in production capacity and underutilization.(5)The decreased site condition of peri-urban cultivated land is the explicit variation of CLQ under the impacts of urbanization,representing the varied morphology and spatial relationships between different land elements.It contributes to the underutilization of cultivated land resources indirectly.The geochemical characteristics of top-soil in a peri-urban area,however,puts more direct influences on the cultivated land use,and they are the recessive variations of CLQ.The urbanization-induced soil acidification,reduction of organic matter and soil nutrient loss are associated with the risk of decline in production capacity,and the soil heavy metal pollution will lead to the risk of polluted agricultural products.In the meanwhile,the decreased stability and the decreased site condition have dually contributed to the risk of land resources underutilization along with reduction of agricultural input,in which way the risk of decline in production capacity is further aggravated.