Spatial interpolation of soil properties based on soil types and trace micro-elements

To develop the methodology for spatialization of large scale soil property, we firstly investigated the relationship between soil properties and environmental factors in Jilin province located in Northeast China. Secondly, with a consideration of soil types, the relevant factors were utilized as co-factors for interpolating soil properties by using the means of Cokriging technique. The results showed that soil pH value, soil organic matter and alkali-hydrolyzable N were generally correlated with latitude and longitude. In details, soil pH value had an obviously negative correlation with longitude (-0.66), available iron (-0.71), manganese (-0.70) and active nitrogen (-0.67); Negative correlation could be found between soil organic matter and soil pH value (-0.58), while positive between soil organic matter and longitude (0.55), available calcium (0.560) and manganese (0.52); in addition, alkali-hydrolyzable N was negatively correlated with soil pH (-0.67) and latitude (-0.57), and positively correlated with longitude (0.57), available iron (0.56) and zinc (0.54); and active phosphorus had an obviously positive correlation with active potassium (0.67) and zinc (0.64). By contrast, the accuracy of Cokriging interpolations used with more relevant co-factors (i.e. trace elements) was obviously higher than the interpolations with other factors (i.e. topographic factors). In addition, the verification results of cross-validation and testing station also prove that accuracy of Cokrigng interpolations is higher than ordinary Kriging.