Modeling Soil Nitrogen Balance Using Geographical Information Systemsand Remote Sensing: The Case of Lower Bilate River Basin, Southern Ethiopia
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Date
2009-06
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Addis Ababa Universty
Abstract
The consideration of soil fertility decline primarily referred to the exploitation of soil nitrogen. Nitrogen
could be added to the soil via Commercial fertilizers, Organic inputs, Biological nitrogen fixation and
Deposition. Conversely, it may be lost from the soil through Leaching, Erosion, Denitirification, Crop
yield harvest and Crop residue removal. The study area was located in lower Bilate River basin within the
Ethiopian rift valley which was characterized by an arid climatic condition with an erratic and unreliable
rainfall characteristic. The core objectives of this research were modeling of the soil nitrogen balance and
the plant available stock soil nitrogen by using a spatially explicit methodology of Remote Sensing and
Geographical Information Systems. Moreover, the uncertainties and source of errors were assessed. To
accomplish the mentioned objectives the study had integrated various primary and secondary data from
various sources. The main inputs were digital soil map, Landsat-ETM+ satellite imagery, SRTM data,
Rainfall data, and Agricultural data. The basic methodology of Stoorvogel and Smaling (1990) was
adapted for soil nutrient balance estimation while the plant available stock soil nitrogen was determined
using simple empirical relations. The research found out that in general croplands are endowed with lower
amount of plant available stock soil nitrogen than non croplands. The addition of Commercial fertilizers
like DAP and Urea were the main inflows in maize land while the fertilizer NPK was the major source of
inflow in tobacco farm. Animal manure was the main source of nitrogen inflow in lands of Sweet potato,
Cotton and Bush and Scattered shrub land. Harvested crop yield was the major source of nitrogen loss in
crop lands. The removal of crop residues was the second most important source of nitrogen outflow in the
area followed by Denitirification and Erosion. The soil nitrogen balance modeling revealed that 6 % of the
area was very strongly depleted (> 40 N), 31 % was strongly depleted (20-40 N), and 61 % was slightly
depleted (< 20 N). Flows such as Commercial fertilizer, Harvested yield and Residue removal were the
possible sources of errors in the final soil nitrogen balance estimation. Land and water management
technologies which maximize inflows of nitrogen while reducing the outflows like addition of
Commercial and Organic fertilizers as well as soil and water conservation structures were the possible
remedial measures that could alleviate soil fertility decline problem in the area.
Key words: GIS/RS, Inflow, Outflows, Soil Nitrogen Balance, Plant Available Stock Soil Nitrogen,
Lower Bilate River Basin
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Keywords
GIS/RS, Inflow, Outflows, Soil Nitrogen Balance, Plant Available Stock Soil Nitrogen, Lower Bilate River Basin