Temporal And Spatial Variation Characteristics Of Soil Organic Matter In Typical Black Soil Region Based On Landsat Imagery

The Black Soil Region of Northeast China is one of the only three black soil areas in the world.It is an important commodity grain base of the country and an extremely important strategic resource.However,due to the influence of natural factors and human activities over the years,black soil is deteriorating,mainly in the two aspects of the reduction of black soil and soil degradation.The decrease in the amount of black soil is mainly due to changes in the nature of land by human activities(mainly refers to the expansion of building land and roads),as well as the change in space area(new and expanded gullies)and vertical(thickness reduction)under natural conditions;The decline in quality is mainly due to long-term over-cultivation,which is manifested in the decline of fertility in black soil,the loss of nutrients in crops and the loss of balance,and the deterioration of soil physical and chemical properties.This study obtained the Landsat images of Hailun County in 1988,2009 and 2016,and used the field soil sampling data in 2009 to analyze the relationship between soil organic matter and its multi-spectral reflectivity by means of professional geology and mathematics software such as Arcgis and Spss.The terrain factor was introduced to establish a prediction model of soil organic matter content.The organic matter content of Helen County in the three-phase remote sensing image was retrieved from point and surface,and the pre diction map of organic matter content distribution was drawn.Combined with topographic information,the temporal and spatial characteristics of soil organic matter in typical black soil regions are revealed from macroscopic and microscopic perspectives.(1)Because of the large time span of this study,two kinds of sensor images are used.There is a linear relationship between the bands of the two sensor images.Correcting the two kinds of sensor images to the same level can make the model established by f itting the reflectivity of TM sensor images in 2009 applicable to OLI sensors in 2016 at the same time.Image.(2)Mathematical transformation of soil reflectance spectra from multi-spectral images can help to eliminate the influence of atmosphere,topography and water,and greatly improve the correlation between organic matter and spectral data.The reciprocal of blue band has a significant correlation with organic matter content of 0.781**.(3)On the same slope unit,the content of organic matter will in crease with the decrease of slope elevation,and the content of organic matter at the bottom of the slope is generally higher than that at the top of the slope;when the slope type changes from concave to convex,the content of organic matter decreases,and when the slope changes from convex to concave,the content of organic matter will also increase.Distribution,the organic matter content of sunny slope is generally lower than that of shady slope.(4)By stepwise linear regression analysis,1/b2(recipr ocal of blue band),24 difference ratio sum(red-blue band difference/red-blue band sum),24 ratio(red-blue band ratio),tanα(6)(angle Tan value at Swir1 band)and SOS(slope variation)are introduced into the model as input variables to make the decision coefficient Rda of remote sensing inversion model.Up to 0.671.Compared with single-band model and multi-band spectral index model,the conclusion that multi-band spectral index model with topographic factors is the most suitable model for the inversion of organic matter in this study is drawn.(5)In the past 30 years,the organic matter content in Helen City has declined slowly,from 4.87% in 1988 to 3.98% in 2016,and the organic matter content in the lower and middle parts of Helen City and the southwest of Helen City has been at a low level from 1988 to 2009.The content of organic matter decreased greatly and rapidly,while the content of organic matter decreased slightly and slowly from 2009 to 2016.(6)The temporal and spatial variation trend and distribution characteristics of Helen’s organic matter content are influenced by climate and topography.It is concluded that Helen City is located in the transition area from hilly area of Xiao Hinggan Mountains to Songnen Plain.Because of the windy dryness in spring and autumn,the climate characteristics of high temperature in summer and cold in winter and the undulating topography of floodplains also lead to organic matter content.The important reasons for the spatial and temporal variation of quantities.