Mapping spatial patterns of soil nutrients in areas under rain-fed wheat

The fertility maps are useful tools to know about land resources. These maps are essential to do a correct fertilizer recommendation, monitoring the changes of soil fertility level and to prediction of toxicity or deficiency of necessary plants nutritional elements in soil. The present report included the works has been done in Golestan province during the year 2008 on research project entitled "Mapping spatial patterns of soil nutrients in areas under rain-fed wheat". The studied areas were under rain-fed wheat cultivation, the total surface area was about 290,000 hectares, and during this period, all area was sampled. Using based maps with scale of 1: 50,000, the area divided into 2900 grids each of them having one-kilometer square area. Using Global Positioning System (GPS) instrument a composite soil sample was taken from the center of any grids and analyzed for Macro and Micro-Nutrients. 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, present and previous crop, etc_were collected and recorded. Based on the national coordinator suggestions samples were analyzed in the laboratory of the Department of Soil and Water Research in Golestan province. After getting the laboratory results, for the above stated data set, an electronic layer was created and after doing interpolation the layers being polygonized. The help of variogram surface operation evaluated anisotropy of the data sets in different directions. Then spatial correlation of each data set was calculated. Doing variogram analysis, spatial variation of the data sets was studied, a suitable model was selected, and finally through point interpolation by the statistical method, kriging technique, the digital map of each secondary nutrient was established.