Biophysical Characterization of Oasis Soils for Efficient Use of External Inputs in Marsabit District: Their Potentials and Limitations

The biophysical site characterization was carried out for irrigated oasis farming in Kalacha, where production has declined to an extent that farmers abandoned their farms and opted for forage production. The objective of carrying out the characterization work was to identify technologies and locally available resources not only for efficient utilization of limited water and nutrient but also to reverse the declining soil quality for long-term production. The land attributes used in differentiating the soils into mapping units were geomorphology, nutrient availability, salinity and sodicity hazards, infiltration rate and drainage conditions for various crops. Productivity index for each soil mapping unit was determined by the regressed relationships between crop production and the soil quality indicators. Unit PIL1 was classified as well-drained, Calcic Solonetz with productivity index of 22%. The most limiting factors were found to be nitrogen and high sodium concentrations. Unit PIL2 comprised well-drained, stratified Salic Fluvisols with productivity index of 26%. The most limiting factors were low nitrogen level and high sodium and salt concentrations. Unit PIL3 had excessively calcareous, moderately drained and strongly stratified soils, classified as Calcaric Fluvisols with productivity index of 21%. The major limitation was nitrogen. Unit PIL4 comprised firm soils, overlying cemented sub-soils with high carbonate concentration, classified as Calcic Solonchaks with imperfect to poor drainage conditions and having productivity index of 12%. The major limitations were poor drainage, high sodium concentration and low fertility status. The soil productivity can be improved by prescribing the required inputs to address the specified limitations.