Digital mapping of soil fertility for agricultural service centers of Golestan province using Kriging method

The fertility maps are useful tools to know about the land resources. These maps are essential to do a correct fertilizer recommendation, monitoring the changes of soil fertility level and also to do prediction of toxicity or deficiency of necessary plants nutritional elements in the soil. The present research was carried out to digital mapping of macro and micro elements as well as some important physical and chemical properties of the soil for agricultural service centers of Golestan province to optimize the use of chemical fertilizers in operating plan pattern. The studied areas were under irrigated and rain-fed wheat cultivation and the total surface area was about 520000 hectares. Using based maps with the scale of 1: 50,000, the area was divided into 5200 grids each having one kilometer square area. Using Global Positioning System (GPS) instrument a composite soil sample was taken from the center of any grid and analyzed for major macro- and micronutrients as well as physical and chemical properties of the soil namely; pH, EC,TNV, sand, silt and clay contents. At the time of sampling, some additional information like latitude, longitude, elevation, owner's name, date of sampling, kind of water resources, possibility of water logging, crop history (present and previous) was collected and recorded. After getting the laboratory results, for the above stated data sets, an electronic layer was created for any particular parameter and after doing interpolation, the layers were polygonized. Anisotropy of the data sets in different directions was evaluated by the help of variogram surface operation. Then spatial correlation of each data set was calculated. After variogram analysis, spatial variation of the data sets was studied and a suitable model was selected. Finally, through point interpolation using kriging technique, the digital map of each parameter was established.