Establishing Digital Spatial Pattern Map of Macronutrients in Soils under Irrigated Wheat in Golestan Province.
Ghorban Ali Roshani and Sohrab Sadeghi. Golestan Agricultural Research Center, Dr. Beheshti street, Gorgan, Iran, Gorgan, Iran
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 also 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 2004 on research project entitled " Establishing digital spatial pattern map of macronutrients in soils under irrigated wheat in Golestan province". The studied areas were under irrigated wheat cultivation and the total surface area was about 220,000 hectares. Using basal maps with scale of 1: 50,000, the area was divided into 2200 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 major macronutrients namely; Nitrogen, Phosphorous and Potassium. 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. 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. Doing variogram analysis, spatial variation of the data sets was studied and a suitable model was selected and finally through point interpolation by the statistical method, kriging technique, the digital map of each macronutrient was established. Keywords: kriging, spatial correlation, macronutrient, variogram analysis