Research About Spatial Variability Of Soil Nutrients In Farmland At Different Scales Based On GIS

In China,scientific management of soil nutrients and rational use of fertilizers are major issues for agricultural development.In the paper,we applied geostatistics combined with GIS to study the spatial variability of soil properties and nutrients contents in cultivated land,to evaluate soil fertility and levels of soil nutrients contents,and to analyze controlling factors of available microelements in the Yueqing city of Zhejiang Province.The main results were summarized as followings:(1) Based on the analytical data of 1209 soil samples,it was found that the contents of soil macroelements(N,P,and K) and Ca,Mg,S,and Si varied remarkably.Available P content showed strong variability,others were moderate.By geostatistics,the ratios of nugget and sill of cation exchange capacity(CEC),total N,total P and total K were lower than 25%,indicating that they had strong spatial correlation.The spatial correlation of pH, organic matter(OM),available N,available P,available K and middle elements were moderate.By using Kriging interpolation,pH,CEC showed decreasing trend from east to west within the city,while OM was massive.The soil in western parts of city was strongly acidic with medium-low level contents of OM and CEC.By analysis of available macroelements,the result showed that the N content was rich in all soils,P and K were inadequate in the soils of some areas,which indicated that phosphorus and potassium should be appropriately increased.Meanwhile,Ca and Mg in soils were rich,soil sulfur content was low to intermediate.(2) Based on the geostatistics analysis of microelements contents in Yueqing city,the ratios of nugget and sill of Fe,Mn were lower than 25%,which showed they had strong spatial correlation.Meanwhile,contents of Mn,Cu and Zn were moderate spatial correlation,indicating that their contents were affected by soil-forming factors and anthropogenic activities.The spatial variability characteristics of microelements in studied region were different.The distribution of Fe and Cu were scattered,Mn,Zn were massive and the distribution of B continuous.In general,the contents of Fe,Mn and Zn were rich, while Cu,B were at moderate and low level,respectively.Soil pH,OM,available nutrients,soil land-use types and soil types are main factors affecting microelements contents in soils.Furthermore,different land-use types and soil types remarkably influenced the contents of microelements.(3) To determine appropriate sampling size,predicted precision of spatial distribution was evaluated by reducing samples using the means of ArcGIS and conventional statistics.The results indicated that the distribution of OM,total nitrogen and microelements could well predict when the sample number was reduced to 50%of original number.In order to improve the prediction precision of available macroelements, we should increase the sampling points as much as possible.According to the nutrients' criterion,there was a notable tendency for spatial distribution of soil nutrients.The studied area could be divided into several nutrients management regions,where different fertilization measures could be applied to provide best services for agricultural production.(4) The analysis of soils from Yuecheng town showed that soil physicochemical properties and N,P,K contents had strong spatial correlation,indicating that their contents was affected largely by soil-forming factors,such as soil materials,topography and climate.As for the middle elements and microelements,Cu had weakly spatial correlation, which may be caused by industrial pollution,while microelements Fe,Mn,Zn and B showed medium spatial correlation.The soils distributed in the western parts of Yuecheng Town were acidic and have medium level contents of organic matter and CEC.The distribution of total P and total K were obviously continuous,decreased from east to west. Total N and available nutrients didn't have obvious disciplinarian,but the contents had reached a rich level.The distribution of Ca and Mg contents were continuous,while S was massive distribution.The spatial distribution of Fe and Mn were massive,while B was continuous obviously,but not for Cu,Zn.The contents of Fe and Mn were rich in soil,Zn content was adequate,while Cu,B weren't sufficient.Topography,soil types and soil nutrients all influenced microelements contents.The soil type remarkably influenced the contents of Mn and Cu,indicating that their contents in paddy soils were much higher than those of red soils.Statistical analysis between microelements contents and soil properties as well as soil nutrients showed that the content of Fe was remarkably influenced by pH, OM,total N,available N and available K.Mn and B were remarkably influenced by pH, available P and available K.Cu was only remarkably influenced by available K while Zn content was weakly affected by soil properties and nutrient contents.