Spatial variability of available nutrients in poplar (Populus deltoides) plantation using different geostatistical methods

It is important to be aware of the spatial dependence structure of different soil properties in natural resources to achieve more production and better management. This study aimed to determine the determining factors controlling spatial variations of macronutrient (NPK) by geostatistics. In the present study, 150 surface soil samples were collected from forests of northern Iran and some variables, including nitrogen, phosphorus and potassium were measured. The half-variance was selected to determine the spatial correlation and the best fitted models on half-variance for variables of nitrogen, phosphorus and potassium were spherical. Also, the effective range for these variables was obtained, which was equal to 530/80, 720/20 and 520/80 meters, respectively. Interpolation was performed using traditional Ordinary Kriging (OK), the inverse distance weighting (IDW) and radial basis function (RBF) techniques using ARC GIS and GS+ software and the accuracy of the distribution map of these variables was calculated using mean absolute error (MAE) and Root Mean Square Error (RMSE). According to the results, the OK technique for the variables of nitrogen, phosphorus and potassium variables was considered as the best interpolation method for estimating the variables in areas where sampling was not performed, because it had the highest accuracy and lowest error.