Spatial Variability And Distributional Simulation Of Cultivated Nitrogen In A Mollisol Watershed Of China

Cultivated land resources is the most basic material of human production activities,is the support and security conditions of social and economic development,and is also the basic elements of regional ecosystem.In the development and utilization of cultivated land resources,the content and distribution of nitrogen in soil are closely related to the nutrient cycle of regional ecosystem,the productivity of cultivated land and the quality of ecological environment.The content of soil nitrogen is too high or too low will affect the growth of crops,causing water pollution and a series of problems.In recent years,to improve the grain yield of cultivated land,the agricultural production and environmental issues due to the unreasonable input of nitrogen has become the constrains of regional cultivated land resource utilization and ecological environment sustainable development.It is of important theoretical and practical significance for improve the regional cultivated land productivity,improve the ecological environment quality to accurately grasp the regional states and spatial characteristics of soil nitrogen.By taking the small watershed as the study area and designing the sampling scheme in the lab.Through field sampling and test analysis in the lab,this paper got the content of total nitrogen and available nitrogen at the surface soil layer of 0-20 cm in a mollisol watershed of China.Based on the classical statistics,geostatistics and “3S” technology,this paper study the spatial variation characteristics of total nitrogen and available nitrogen in cultivated land,and study its model simulation and influence factors of spatial distribution using the Moran's I,semivariance function model,co-kriging,regression kriging,geographical weighted regression kriging,correlation analysis,regression analysis and variance analysis in a mollisol Haigou watershed of China.The main conclusion are as follows.(1)The content of total nitrogen and available nitrogen at the surface soil layer of 0-20 cm were 0.96-5.50 g.kg-1 and 34.02-207.09 mg.kg-1,the standard deviation were 2.17 and 29.60,at a high level and medium level respectively,the spatial variability of total nitrogen and available nitrogen were moderate.(2)The spatial autocorrelation coefficient of total nitrogen and available nitrogen were 0.15 and 0.29 in Haigou watershed,existed spatial autocorrelation differently,and the spatial autocorrelation was a big different in each direction,the autocorrelaton characteristics of total nitrogen and available nitrogen in the East-West direction were more obvious.The semivariance theory models were Gauss model respectively,the ranges were 900 m and 1282 m respectively,the C0/(C0+C)of total nitrogen and available nitrogen were 0.03 and 0.114.The spatial variations oftotal nitrogen and available nitrogen was mainly affected by soil parent material,topography and other structural factors,human activities(farming systems,fertilization practices.etc)had little influence on it.The variation of the East-West direction was dominant in the spatial variation of the two elements.The East-West direction was also the key area need to analysis and exploration in the future research on soil nutrients in Haigou watershed.(3)Geographical weighted regression kriging could effectively improve the simulation accuracy of the nitrogen spatial distribution,and could have a further popularization and application.The simulation results shown,the high value of total nitrogen was mainly distributed in the transition zone of hill and plain,the central town and other small areas in Haigou watershed,the low value was in the more concentrated area of paddy field in the west.The changes of high value and low value were flat,and were similar to changes of land use in the same direction.The high value of available nitrogen was mainly distributed in the eastern mountainous area,the low value was in the more concentrated area of arid in the middle.Also,Available nitrogen performed another kind of trends,and was low in the middle area,while was high in both sides of the watershed,and the distribution was closely related to the terrain topography.During the course of simulation,the interpolation errors was transferred to the further interpolation of the residuals generated by geographical weighted regression.It was an important step to further improve the accuracy of interpolation and reduce the error,there needed to be a further discussion.(4)The slop was very significantly positively correlated with spatial distribution of total nitrogen,and the plane curvature was significantly negatively correlated with spatial distribution of total nitrogen.Elevation and slope position were very significant positive correlation with spatial distribution of available nitrogen,profile curvature was significantly negatively correlated with spatial distribution of available nitrogen.The spatial distribution characteristics and the law of nitrogen content could be explained effectively by using the significantly index as the auxiliary variable.Rivers,residential and other elements had a obvious effect of distance on the spatial distribution of total nitrogen and available nitrogen,and showed a strong regularity,these elements had certain effect on the spatial distribution pattern of total nitrogen and available nitrogen.The land use type and slop position had a effect on the content of total nitrogen and available nitrogen,and had a big difference in it.(5)The distribution of nitrogen in soil and the environment factors such as topography were a complex system,with the increase of the range and intensity of human activities,the distribution of nitrogen was more and more disturbed by human activities.It was the key content to consider more human activities in the further study of spatial variability of soil nutrients,distribution simulation and impact mechanism of distribution.The study results could serve the formulation of regional fertilization and farming model in the macro level,and guide the agricultural production and environmental management in the study area quantitatively and orientation.This study could provide the basis information for the improvement of cultivated land quality and ecological environment in the study area,and furtherpromoted the coordinated development of grain productivity and ecological environment protection in the black soil region.