Assessing soil fertility level in a GIS environment : the case of Wonji Shoa sugar factory (WSSF) estate farm in Ethiopia

The study was conducted to assess soil macro nutrient level and the general fertility rate in GIS environment for the case of Wonji Shoa Sugar Factory estate farm in Ethiopia. For the study a CAD format map and 131 sample soil macro nutrient level laboratory analyses were collected; these include the sample soil laboratory analysis of soil texture, pH, organic carbon, total nitrogen, available phosphorous, carbon to nitrogen ratio, calcium carbonate content and yield produced per hectare. These samples were used as major input parameters. After the data collection to achieve the above stated objective data processing was done in different stages. At the first and second stage the necessary pre-preprocessing of the data, interpolation and reclassification of soil macro nutrient layers based on their effect on the soil were done in Esri ArcGIS geostatistical environment. For the purpose of this study the interpolation methods IDW and Kriging were applied by subdividing the sample data in to training set (111 sample points) and test set (20 sample points). After interpolation computed with the training data set, for each interpolation model, the error statistics of each interpolation result were properly evaluated. At the third stage, the ranking of each parameter were cared out by using the a priori information of decision makers. The weight of each soil macro nutrient factors were computed in IDRISI software, and based on those results the weighted overlay analysis of the study area was conducted, in addition to that the outputs were generated in different map layouts. The fertility level of the estate farm is identified and presented in maps by rating the fertility as high, medium and low. The result illustrates that around 49% of the study areas are having medium and high fertility level and the remaining 51% of the areas are having low fertility level. Besides, areas which need additional treatment to improve the productivity of the plantation area were identified and the performances of the existing fertile area have been described in terms of macro nutrient level.