Availability of phosphorus in the coffee soil of South West Ethiopia
1996
Paulos Dubale (IAR, Addis Abeba (Ethiopia))
The bulk of the coffee soils in south west Ethiopia is classified as Nitosols. Phosphorus (P) is the limiting nutrient in this and other types of soils in the region. The status of P in soils from Melko, Tepi, Goma, Kosa, Suntu and Gumer was investigated. Available P (Bray I) was below 11 ppm for the top 30 cm soil for all the sites tested except goma II and Tepi. However, soil samples collected from the sami area with no history of fertilization indicated very low level of P. All of the soils tested had high Fe bound form of P (Fe-P). The P adsorption isotherms were studied for the six soils. Goma II soil required the least amount of P to reach a minimum threshold in solution followed by Tepi soil when compared with the other soils and the soil from Kosa had a distinct multiple phases of P adsorption by the Langmuir plot. The concentration of exchangeable P determined in the samples without added P in soils from Melko and Kosa appeared high and varied significantly. The sources of P fixation in these soils appear to be mainly because of the high concentrations of iron oxides and hydroxides.
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