Detailed study on soil fertility assessment based on the understanding of the soil system are not available for the most part of Ethiopia. With the cognizance of this fact, the present study was conducted to assess the soil fertility status and to prepare the fertility map of Argo-Gedilala Sub watershed in Dugda District, Central Rift Valley of Ethiopia. Eighteen composite soil samples (0-20cm depth) were taken for fertility assessment of the soil from the land mapping units of the subwatershed and mapping the status of selected soil fertility parameters was done using ordinary kriging technique in ArcGIS 10 software. The bulk density is at an acceptable range 1.3 to 1.4 g cm-3 for mineral agricultural soils. The soil organic matter contents of LUs (04, 05 and 06) 680.47 ha (64.77%) in the study area can be categorized in the range of low soil organic matter content and LUs (01, 02 and 03) 369.31 ha (35.23%) can be categorized in the medium range at the sub-watershed. The average percent total N content of the LUs (02, 04, and 05) 567.7ha (54.05%) were found to be low; LUs (01, 03 and 06) 482.61ha 45.95%) were found to be moderate. The mean available P of soils of LUs (04and05) 443.17 ha (42.19%) was categorized as very low range and LUs (01, 02, 03 and 06) 607.15 ha (57.82%) classified as low range. Exchangeable Ca2+, LUs (01, 02, 03, 05 and 06) 824.88 ha (78.55%) were very high while LU04 which covered an area of 225.44 ha (21.46%) were rated as high. The soils of the study area had low organic matter, available P and total nitrogen content, which can be seen as production constraints of all cultivated lands. To overcome the identified limitations, increasing the organic matter levels through continuous application of manure and/or compost should be integrated with chemical fertilizers.
Key words: Fertility status, land-mapping units, ordinary kriging.
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