The consideration of soil fertility decline primarily referred to the exploitation of soil nitrogen. Nitrogenrncould be added to the soil via Commercial fertilizers, Organic inputs, Biological nitrogen fixation andrnDeposition. Conversely, it may be lost from the soil through Leaching, Erosion, Denitirification, Croprnyield harvest and Crop residue removal. The study area was located in lower Bilate River basin within thernEthiopian rift valley which was characterized by an arid climatic condition with an erratic and unreliablernrainfall characteristic. The core objectives of this research were modeling of the soil nitrogen balance andrnthe plant available stock soil nitrogen by using a spatially explicit methodology of Remote Sensing andrnGeographical Information Systems. Moreover, the uncertainties and source of errors were assessed. Tornaccomplish the mentioned objectives the study had integrated various primary and secondary data fromrnvarious sources. The main inputs were digital soil map, Landsat-ETM+ satellite imagery, SRTM data,rnRainfall data, and Agricultural data. The basic methodology of Stoorvogel and Smaling (1990) wasrnadapted for soil nutrient balance estimation while the plant available stock soil nitrogen was determinedrnusing simple empirical relations. The research found out that in general croplands are endowed with lowerrnamount of plant available stock soil nitrogen than non croplands. The addition of Commercial fertilizersrnlike DAP and Urea were the main inflows in maize land while the fertilizer NPK was the major source ofrninflow in tobacco farm. Animal manure was the main source of nitrogen inflow in lands of Sweet potato,rnCotton and Bush and Scattered shrub land. Harvested crop yield was the major source of nitrogen loss inrncrop lands. The removal of crop residues was the second most important source of nitrogen outflow in thernarea followed by Denitirification and Erosion. The soil nitrogen balance modeling revealed that 6 % of thernarea was very strongly depleted (> 40 N), 31 % was strongly depleted (20-40 N), and 61 % was slightlyrndepleted (< 20 N). Flows such as Commercial fertilizer, Harvested yield and Residue removal were thernpossible sources of errors in the final soil nitrogen balance estimation. Land and water managementrntechnologies which maximize inflows of nitrogen while reducing the outflows like addition ofrnCommercial and Organic fertilizers as well as soil and water conservation structures were the possiblernremedial measures that could alleviate soil fertility decline problem in the area.rnKey words: GIS/RS, Inflow, Outflows, Soil Nitrogen Balance, Plant Available Stock Soil Nitrogen,rnLower Bilate River Basin