Effects Of Cultivation History On Spatial Distribution Characteristics And Mapping Of Soil Organic Carbon In Arable Land In Northeast China

Soil carbon pool is the largest carbon pool in terrestrial ecosystem.Its dynamic change and spatial distribution play an important indicating effect on soil quality and have a great impact on global climate change.The soil organic carbon(SOC)pool in arable land soil has a great significance in maintaining the soil fertility,protecting environment and agricultural sustainable development.Researches show that soil organic carbon has spatial heterogeneity.The spatio-temporal variability of SOC has attracted more and more attention with the development of agriculture and the requirement of land use management.Accurately estimating SOC and analyzing its spatio-temporal variability and the influencing factors is of crucial importance.SOC pool is not an isolated ecosystem which will be affected by the natural environment and human factors.On the regional scale,various factors are closely related to each other.Human factors are the dynamic factors that affect the change of soil carbon pool in arable land,which is difficult to quantify.In a certain period,it is possible to overtake the natural factors to become the dominant factor of affecting the change of soil organic carbon pool in regional arable land.Therefore,it is more important to study the spatial variability of SOC with long time scale.Previous studies on soil profile organic carbon density(SOCD)of large-scale arable land mainly considered natural conditions,but rarely considered the history of reclamation,especially the long time series of more than 100 years.The study targeted the arable land in three provinces of Northeast China.According to the reconstruction data of arable land in the historical period,we revise the distribution pattern of arable land in the historical period,then obtain the length of cultivation of arable land.Based on the purposive sampling method,233 profiles and 1173 soil layer samples were collected.By means of Remote Sensing and Geographic Information System,using statistical methods and model method,we study the spatial variation characteristics and influencing factors of SOC content in 0-100 cm depth under long-term scale in Northeast China,to reveal the change rule of SOC in arable land,and illuminate the influence of natural factors and human factors on the SOC in arable land.Finally,we predicted and mapped the spatial distribution of SOC content in the surface layer and SOCD of 1m,in order to understand the impact of human activities on SOC better,and to provide a scientific basis for the rational formulation of arable land soil protection and management policies and the promotion of soil carbon sequestration.The main conclusions of the study are as follows:(1)By collating and analyzing the data sets of historical arable land reconstructed by previous scholars over the past 300 years,the quantity changes of arable land and its spatial distribution in Northeast China were clarified and revised from the Qing Dynasty,the Republic of China period,and the People's Republic of China to now.We selected the time section of arable land changes caused by important historical events,combining with the succession of ecosystem in the study area,the cultivated history of arable land in the northeast area is divided into seven times series,T1(2005-2015),T2(1978-2005),T3(1949-1978),T4(1895-1949),T5(1815-1895),T6(1715-1815),T7(1644-1715),respectively.Then we obtained the map of length of cultivation of arable land in the last 300 years in northeast China,and on this basis,we analyzed the characteristics and driving force of the change of the arable land resources in this region.(2)The statistical analysis of the factors affecting the SOC in arable land in Northeast China shows that the SOC content in northeast China is significantly negatively correlated with the mean annual temperature,and is positively correlated with the mean annual precipitation.The SOC in the plain area with lower elevation is higher than that in the hilly area.With the increase of the length of cultivation,the lower the content of SOC was.The effect of these factors on surface layer(0-30cm)was obvious greater than that on subsurface layer(30-50 cm)and substratum layer(50-100 cm).(3)By establishing the Boosting Regression Tree(BRT)model,it showed that the length of cultivation can explain 76% of SOC variability,and its relative importance is 23% in all variables.In the reclamation process of arable land in northeast China in the past 300 years,the SOC loss rate of the whole area in surface SOC of arable land is about 45%,and the SOC content showed a downward trend from north to south.(4)Based on the knowledge of soil genesis,combining with all variables,the equal area spline function and BRT model were used to predict the vertical distribution of SOCD in the 100 cm profile of arable land in northeast China.As a key variable affecting the spatial distribution of SOC in arable land,the length of cultivation was added to the SOC mapping to improve the prediction accuracy,which provided the basis for the estimation of soil organic carbon pool and agricultural management in the region.